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Pool Leak Detection

Leaking swimming pool This article is a swimming pool leak detection guide to help you understand the process of how to find a leak in a swimming pool. This subject is one of the most heavily searched for subjects relating to swimming pools - and for good reason. If you have ever had a leak in your pool before you already know how difficult, time consuming and expensive it can be to resolve this problem. Swimming pool leaks can be very elusive to find even for seasoned professionals in the industry. This is why many pool builders and swimming pool service companies offer little or no leak detection services. This is also why there are companies that specialize in only pool leak detection. In many cases these companies do not even fix the leaks that they find instead operating more as a "leak detection" service as opposed to a "leak repair" service. This may seem counterintuitive for pool owners who seek the assistance of professional leak detection companies. Once you hire the leak detection company and they locate the leak you still need to have a pool service or repair company come and actually perform the required repairs.

Why do leak detection companies not also fix pool leaks themselves?

Finding a pool leak is hard to do. Even with more advanced equipment than was available just 20 years ago there is still a fair bit of guesswork involved with finding a leak in a pool. In the most simple of terms, most pool service companies do not make a profit on leak detection jobs. Leak detection specialists, while more capable than the average pool company, still fail to locate the leak in the pool more often than not on the first try. To combat this problem leak detection companies will offer a guarantee on their work, which means that if the leak is not where they thought it was they will often come back at no charge and try again. Meanwhile you had to pay a company to come and cut open your pool deck and dig down to where the leak was suspected to be. While the leak detection company does not charge to come and locate the leak a second time, the pool company that did the dirty work of digging up the leak location does. If the leak is elusive, or if there are multiple leak locations complicating the detection process, you could find yourself buried in labor bills and still have a leak in your pool. While this certainly is not the case for every pool leak detection job, as a veteran of the industry this is a story that I have witnessed time and again. When you have a leak in your pool you will have a very difficult time getting a company to take responsibility of the situation. They know that there is a high chance that the leak will be difficult to find, and most likely they will not end up being able to charge for the actual time that they will need to spend working on your pool to find and fix the problem. To add to this, the leak detection person is usually one of the most experienced and valuable people on staff and taking them away from higher profit jobs just does not make sense.

pool leak detection In many cases pool owners are left to try to find a leak in their pool on their own. Some pool owners may have tried to hire a company to look into the problem unsuccessfully, while others may have already paid for leak detection services but the pool is still leaking. At the end of the day the responsibility of the pool rests squarely on the owner of the pool. If you have a leak in your pool then it needs to be fixed. You should not continue to operate a pool with an active leak, nor should you drain your pool if it is leaking as this can often make the situation much worse. This is the kind of situation that gives pool owners nightmares. A leak in a pool is almost certainly causing additional damage to other components of the pool and can even cause damage to adjacent buildings, your property, or your neighbors property. Hopefully this is not the case for you. Hopefully you found a local leak detection company that is great to work with, is affordable, and is efficient at finding and fixing your leak. Unfortunately for most pool owners who have discovered a leak the process will not be this smooth. There is one piece of good news in all of this doom and gloom - finding a pool leak is actually not that hard and something that you, as the pool owner, can likely do yourself. Even if you can not find the leak you can at least gather information about how the pool leaks that may end up helping you further on in the process.


How To Find A Pool Leak

Wait, you just said that pool leaks are so hard to find that most pool companies can not find them and then you said that a pool leak is easy enough to find that a pool owner can do it themselves...seems like quite a contradiction!

To clarify, the reason why a pool owner can find a leak that a pool company can not find is actually very simple. The pool company could likely find the leak if they spend enough time testing different parts of your pool looking for it. The problem is that you will not be happy with the massive labor bill you receive for the amount of time they needed to spend locating and fixing the leak. The process of testing a pool for leaks is one that takes time, and must be completed in stages. What this means is that a pool will need multiple return trips from a service technician to complete a process of elimination style of tests. If the leak ends up being somewhat elusive or hard to find this could result in dozens of return trips to your house.

Do all pool leaks require dozens of visits from leak detection workers? No, certainly not, but enough of them do that many pool companies are wary about taking on leak detection work. What many service companies are now doing is enlisting the pool owner to conduct different stages of the testing on their own (following instruction from the pool company) in order to reduce on the number of trips they will need to make to your property. The more information that a pool company is able to learn about your pool, and specifically the symptoms of how your pool is losing water, the better their ability to efficiently diagnose and locate the leak. Many of the "leak tests" that a pool company will do as part of the process of elimination to find your leak are actually easy enough that you can do them yourself. While the average pool owner many not be able to find and fix every pool leak, there are many pool owners who will get lucky and find the leak themselves just by conducting some simple tests. Even a simple test can provide huge insight as to where the pool is leaking - with a little luck and some help from the information on this page hopefully you can find and fix yours.





Pool Water Evaporation

Anyone who has ever worked in swimming pool leak detection knows that pool leaks are sometimes just evaporation that the pool owner mistakenly believes to be an active leak. The first step in leak testing any swimming pool is to figure out if the pool is actually leaking. A surprising amount of "pool leaks" are actually just periods where the water is evaporating quickly due to environmental conditions. If you are new to owning a pool then you will not be familiar with evaporation rates or what you should consider as normal evaporation rates for your pool. The actual amount of water that your pool will lose to evaporation will be unique to your pool. Factors such as your geographic location, ambient temperature, water temperature, direct sunlight and cross winds will all have an effect on your evaporation rates as will whether you use a solar blanket cover at night.


pool bucket test I can tell you that in my geographic area about 1/4" of water loss per day would be normal however this is not helpful to you. You may live in an area with much higher rates of evaporation. This is why the bucket test is used to determine if a pool is leaking or if the pool is simply losing water through evaporation. The reason why the bucket test is so important is that is removes the external factors that make your evaporation rates unique. The bucket test allows you to measure the rate of water loss in your pool versus the rate of evaporation in your pool. This is the first test that every pool owner with a suspected leak should do. If you are getting inconclusive results with your test then something as simple as knowing the temperature from one day to the next can help you to accurately interpret the results of your tests.
Bucket Test:
Using an open top container such as a plastic juice pitcher you will sit the container inside of the pool such that it is partially filled with water. My preferred method is to use rocks in the bottom of the container and then sit the container on a stair or ladder step such that part of the container is below water level and part is above. You then add water into the container until the water inside the container and the water level in the pool are exactly the same. Wait 24 hours and then check to see if the water level in the pool is lower than the water level in the container. The difference between the two would be rate of water loss in your pool. If you do this test and the water level in the pool always matches the water level in the container then you do not have a leak in your pool - your water loss is a result of evaporation. Using a solar blanket at night over the pool will dramatically reduce how much water your pool loses through evaporation.


When you are doing the bucket test it would be a smart idea to record the weather patterns during this time period. The outside temperate (at both day and night) as well as cloud cover (direct sunlight the pool gets) as well as the amount of wind that you have. Most importantly you need to note if it rained or not as rain will likely invalidate your test results.


Obvious Signs Of Damage

sinking pool deck If your pool is leaking more than evaporating then the next step in the process of elimination is to thoroughly inspect the pool for damage. This is a step that an experienced pool technician will have a distinct advantage over a pool owner. There are many subtle (and some not so subtle) symptoms that a pool is leaking in a specific spot. You may not even notice something minor that a more experienced eye may see. To combat this you must be very thorough when inspecting your pool for damage.

leaking pool skimmer Any part of your pool that shows signs of damage or wear is highly suspect when it comes to looking for pool leaks. When a pool leaks it will cause damage to the surrounding structures and some of this damage may be visible. Pool decks that are sinking or have cracks are a major symptom of a potential leak. Rust forming around skimmer and return ports, holes in your liner that have been patched, cracks in the pool floor, broken fittings - any signs of damage to the pool should be noted and heavily scrutinized to see if they are the cause of the leak or perhaps a symptom of a leak in an adjacent location. As an experienced pool leak detection expert this is the first thing that I am looking for when I inspect a leaking pool. In the event that you do discover some signs of damage, or you have an area that you suspect to be leaking, then the first step that you should take is to dye test this area.


Swimming Pool Dye Test

If you have a location in your pool that you suspect is leaking then the first step you should take is to test the area with dye. Most pool owners do not understand how a dye test works on a swimming pool but sufficed to say that it is not a definitive test in most cases. Only in the most serious of leak situations should you be able to make a definitive judgment about the presence of a leak with a dye test.

To dye test a swimming pool the goal is to release a small amount of dye in the immediate location where a leak is suspected. In order to do this the pool circulation system must be turned off and there should be little or no wind causing movement in the pool water. You want the pool water to be as still and as calm as possible when you are doing a dye test. Even the movement of putting your arm into the water can make the results of the test hard to evaluate. So, being as still as possible you will attempt to release a steady stream of dye into the area surrounding the suspected leak. The dye will have the tendency to stay together and will float gently with the subtle motion of the water moving. If a leak is present then you will be able to see the dye actively being pulled out of the pool through the leak. Dye testing is very useful around flanges such as lights, steps, skimmers and returns where you are able to get close enough to release the dye and monitor its movement in the water. Cracks in the floor of concrete pools, or suspected leaks in the main drain of your pool (in the bottom of the deep end) are not ideal for dye testing unless you have scuba equipment which will allow you to get close enough to test these areas.



While leak detection with dye is often not definitive in terms of finding leaks, this is a great tool and an easy test that pool owners should have at their disposal. If you are ordering leak testing syringes online be sure to order a few of them. They do not go bad and you will go through them very quickly when testing the pool. As a word of caution to pool owners trying a dye test for the first time - you are very likely to be disappointed with the results. It is very difficult, and often not possible, to find a leak using only dye. Even when you do find a leak with dye you will not likely be confident enough with the test to say with certainty that you found the leak. Use the dye testers as a supplemental tool in your leak detection kit but do not expect them to be a magic beacon pointing at your pool leak unless you have a massive amount of water loss.


Isolate The Pool Leak

Here is where this leak detection tutorial starts to get into more advanced leak detection tests. The bucket test and the dye test, along with a solid visual inspection are the first steps that most people will take to try to find a leak in your pool. When these quick and easy tests fail to locate the leak then you need to begin to break the pool down into sections in order to narrow down where the leak might be coming from. Not every part of your pool can be definitively tested for leaks - sometimes you will only know where the leak is because you have tested every other possible source for the water loss. Due to this it is very helpful for the leak detection process to begin to isolate the different parts of the pool in order to reduce the guesswork involved with finding the leak. If you can find the general location for the leak then you can focus your time and energy testing these specific locations.

When looking at a swimming pool as a whole, you can break it down into two main components which are:

1)The pool structure
2)The pool plumbing system

The structure of a swimming pool refers to the main body of the pool itself. This would include the interior surface of the pool as well as any fixtures installed into the pool. The plumbing system is everything that is located outside of the main body of the pool. Determining which of these main components is leaking will go a long way towards finding the leak in your pool.

Determining whether the pool is leaking through the structure or through the plumbing system can be done by plugging all ports in your pool with winterization plugs. By turning off the circulation system for the pool and plugging the skimmer and return ports you can isolate the body of the pool from the plumbing system. If you have a main drain in your pool then this complicates this test as you will either need to swim down and plug off the main drain line, or do the test without plugging the main drain. With all of the pool suction and return lines plugged simply let your pool sit for 24 hours and compare the rate of water loss to that of what you lose when the ports are not plugged. If the pool loses no water with the returns and skimmer lines plugged, but does lose water once you remove these plugs, then the leak is located somewhere in the plumbing lines for your pool. If the plumbing lines for the pool are leaking then you will need to skip ahead to the section on pressure testing the plumbing system. If the pool still loses water with the returns and skimmers plugged then this means that the leak is in the structure of the pool somewhere (or it is in the main drain if you were not able to plug yours as part of this test).


Pool Structure Leaks




Leaks in the pool structure refer to leaks anywhere within the body of the pool (not in the plumbing system). Leaks within the structure of a pool are difficult to diagnose as there is not much in the way of definitive testing that you can do to find them.


If you have determined that you have a leak somewhere in the structure of your pool then the process of finding it is simply by close inspection. It is also helpful to know how swimming pools tend to leak as this can help you in focusing on the most likely areas.

leaking pool light Leaking pool lights - Leaks from swimming pool lights are one of the more common structural leak locations in a pool. Light canisters (niche) are attached to the pool wall to receive the light assembly. Lights can leak in a number of different ways but the most common would be through the electrical connection on the back of the niche. The electrical connection point on a pool light niche is prone to failure and not something that is easy to fix unless you are able to dig up the light from the back side of the pool wall. Light niches also can crack from age or from freeze and thaw conditions in the pool. If this is the case you should be able to see cracks in the niche upon close inspection and a dye test may confirm if the cracks are actively leaking. Inspecting a pool light is not the easiest thing to do since they are so far below the water level of the pool. Using swimming goggles to get close enough for a visual inspection is your best bet. In some cases you simply may not be able to see inside the niche to inspect it. If you suspect that your pool light is leaking though the electrical conduit then you should try to seal the conduit with this electrical conduit sealer. This product does not harden like epoxy so you can reach into the light niche and pack the electrical conduit hole without causing future problems for yourself. If the light is leaking through the electrical conduit connection then you may be able to slow or stop the leak this way. Failing this you will need to dig up and expose the back side of the light niche to properly inspect and repair it.

Leaking skimmer - Leaks in the pool skimmer would be part of the pool structure (not to be confused with leaks in the skimmer plumbing line) and are a very common cause of water loss in swimming pools. Skimmer bodies can crack with age, chemical damage or improper winterizing. If you have a crack in the body of your skimmer then this is almost certainly leaking water. You can try to dye test the skimmer cracks to see if you can get a definitive leak diagnosis or you can simply try to repair with some pool epoxy. Replacing a pool skimmer is a big job and one that often leads to needing to do other work as well so replacing a broken skimmer on a pool is not always an option. To learn more about how to replace a broken pool skimmer and why doing this often leads to other work you can read this article on pool skimmer replacement. If you have a vinyl liner pool then the skimmer can also leak through the flange and gasket that compresses it to the pool liner. If you suspect a leak in this area on a vinyl pool then you should check that each screw in the faceplate is very tight. Any loose or spinning screws are guaranteed to be losing water. On a concrete pool the skimmer is different and is usually encased in a solid cube of concrete. While this will often prevent water from escaping this area, it will not always be enough. If there is even the slightest potential for water to escape the pool system then it will find a way. On a concrete pool skimmer this will most often be through the face of the skimmer itself. Water will chase along the sides of the skimmer itself and escape the pool. If you suspect that your skimmer is leaking then try to tap on the throat lightly with a hammer. The throat of a concrete pool skimmer should be completely encased in concrete. If you tap and the skimmer sounds hollow, especially on the bottom side of the skimmer throat, then this is likely from a long term slow leak in this area of your pool.

Leaking returns - Leaks in pool return lines are one of the most common causes for a leak in swimming pools. Right now however we are looking at structure leaks so for this section we are not talking about the return lines themselves, but instead the return flange inside of the pool where the return line terminates. In a vinyl liner pool it is very common to have leaks through return gaskets and fittings if the gasket orientation was not installed correctly to begin with, or if the flange itself has become cracked or damaged over time. Similar to vinyl pool skimmers, if there are any screws not installed, not tight, or spinning in the hole, then this is a guaranteed leak location. On a concrete pool the returns are inclined to leak in a different way. In a concrete pool the water will try to escape the system by tracing along the pipe penetration through the concrete wall of your pool. To combat this many pools have "water stops" installed inside the pool wall which stop the water from being able to trace back along the pipe. Older pools especially are prone to having problems in the return locations from insufficient concrete being packed underneath of the return pipe. Shotcrete and gunite pools both involve a spray process for installing the concrete. Due to the way that pools are built there is a specific weakness for the underside of pipe penetrations to not get packed with concrete correctly. This will start as a slow leaching leak that would be imperceptible, but over time the passage of water through this location will weaken the concrete here and will eventually one day turn into a more serious, active leak location. If you have a leak under the return ports in your concrete pool then the best way to fix this would be to lower your water level below this area and use a chipping hammer to remove any loose concrete. Quite often this will end up exposing a hole under the return line which has been there since the pool was originally installed. You can pack the area with a water stop hydraulic cement product, or you can also use a urethane sealant, or both.

Main drain leaks - A leak in the main drain of your pool is not a situation that you want to have. The biggest problem is simply that the main drain is located on the floor of the deep end of the pool and can be very difficult, or impossible, to access. If you can not get close enough to your main drain to inspect it or plug it off for testing then you will have a very hard time trying to determine if this is the cause of your leak. In many cases troubleshooting the main drain is simply a matter of testing all other components of your pool. By using this process of elimination you can identify if the main drain is likely the cause for your water loss. Main drains tend to leak in two ways most commonly. The main drain has a port on the bottom of it which is intended to house a hydrostatic relief valve. This valve is a one way, spring loaded valve that is designed to allow water into your pool should there be an elevated water pressure under the pool due to high water tables. This is the safety protection that all concrete and fiberglass swimming pools need to prevent from lifting however many vinyl liner pools have hydrostatic relief valves also even though they technically do not need them the same way concrete and fiberglass pools do. A hydrostatic relief valve is operated by a mechanical spring and as such the spring can deteriorate, rust and fail over time. This could easily account for a leak in the main drain of a pool. It is also fairly common for hydrostatic relief valves to get stuck open from debris obstructing the valve from closing. If this happened then it is possible for your entire pool to drain out through the bottom of the main drain.

Equalizer line leaks - Another very common way that main drains leak is through the equalizer line. The plumbing pipe on most pool main drains does not actually connect directly to the suction lines for the pool. Often the main drain has a non-pressurized equalizer line that connects from the main drain port to one of the skimmer ports on the bottom of the skimmer. In this common configuration the main drain pipe does not actually experience any suction pressure from the filtration equipment. Instead the equalizer line allows water into the bottom of the skimmer should the water level in the pool fall below the mouth of the skimmer. Without this feature it is very likely you would burn out your pool pump if the water in the pool ever dropped below the mouth of the skimmer (which is only a few inches below the normal operating level of your pool). Having an equalizer line from the main drain to the skimmer is the best way to protect yourself from this problem. The only concern is that should you ever develop a problem in this pipe then you will have little recourse to fix it. In fact the equalizer pipe that connects from the main drain to the skimmer is the single most likely pipe on your pool to fail. The reason why is simply how inaccessible this pipe is. Even during full scale pool renovation projects this equalizer line is often not replaced. Either the line continues to function without leaking or it will simply be plugged off in both the main drain as well as the skimmer. The pool will continue to operate more or less effectively, just that you must be careful to not let the water level of your pool drop below the mouth of the skimmer or you risk burning out your pump. If you have leak in this location of your pool then the repair process is the same. You must plug the port in the main drain as well as in the bottom of the skimmer to isolate this equalizer line from both ends. It is not easy to swim down and plug a main drain inside a pool full of water but it is possible. If you are not able to do this yourself then you should not have much trouble finding a pool service company or diver to plug it for you.

Structural leaks (vinyl liner pools) - Structure leaks are very common in swimming pools. In addition to the individual items such as the skimmer, returns, lights and main drains already discussed, leaks through the physical structure of the pool itself are very common. On a vinyl liner pool a structure leak means that you most likely have a hole in the liner somewhere (or multiple holes). You can lose a surprising amount of water through a small hole in your vinyl liner. The process of finding a hole in your liner involves more inspection than anything else. While there does exist electronic tools for helping to locate leaks in a vinyl liner, most holes will be found simply by looking in the most common areas. A hole in a vinyl liner will typically be crescent shaped and around 1/4" in length. To find holes like this you would simply use a systematic approach to inspecting the liner. Most commonly this would be done from inside the pool while wearing goggles to help you see clearly. Start by inspecting the walls and give specific attention to where the walls meet the floor in the shallow end (the cove) as well as in the corners of the pool. Use your hands and feet to help you feel for any imperfection in the liner and then inspect these areas closely. Holes in the vinyl liner can come from broken maintenance equipment with sharp edges, automatic vacuum cleaners, sharp toenails or swimwear that has buttons, clasps or other metal parts. Once you locate the hole (holes) in your liner then a simple vinyl liner patch kit is all you need to fix the leak. A slightly less common way that vinyl liners can develop a leak is though a separation of the welded seams. A vinyl liner is made by welding sheets of vinyl together. This used to be a process done by hand by skilled vinyl welders however most liner manufacturers have now switched to a machine controlled process. A vinyl seam is most likely to separate at the point the liner is first installed. If you are searching for a leak in a brand new liner installation then be sure to heavily scrutinize the seams in the vinyl. Run your hands over them to see if you can feel any loose sections that might indicate a seam separation. Older liners can also experience a seam separation however this would be less common since the liner tends to be under even pressure once it has the weight of water on top of it.

Structural leaks (concrete pools) - If you have a concrete pool with a suspected structure leak then this is more of a concern, and a harder leak to find than with a vinyl liner leak. In a concrete pool the first thing that you should look for is the presence of any cracks in the interior finish. Cracks in a concrete pool are bad. If you have a crack then it is either just a crack in the 1/2" thick plaster layer, which is not as big of a problem, or it is a structural crack that penetrates through the concrete shell of the pool. If you have cracks in the interior surface of your pool then you can attempt to dye test them to see if they are actively leaking. Another reason why concrete pools lose water is because concrete is a porous material. Even very dense mortar finishes like pool plaster are only water resistant. All concrete pools leak - or more accurately all concrete pools leach water. Water absorbs into the concrete as part of the normal operation of a concrete pool. As the pool ages and the interior surface becomes less and less water resistant then water will leech into the concrete shell faster and faster. Quite often with concrete pools, especially older concrete pools with interior surfaces past their service life, the water loss will be the sum total of water leaching through the interior surface and into the shell over the entire surface area of the pool. If you have a concrete pool with a persistent leak problem and the interior surface of the pool is over 10 years old then there is a very decent chance that your water loss could be explained by water leaching through the finish of your pool. A new plaster interior surface is quite expensive and many pool owners will try to put off a new plaster as long as possible. Painting of concrete pools is something that is often done as a low cost alternative to new plaster but is inferior to plaster in every way. If you choose an epoxy paint or rubber based paint then you will no longer be able to plaster the pool without sandblasting first. Most pool experts agree that painting a pool with epoxy paint (or rubber based paint) is not worth the investment and you would be further ahead to simply replaster the pool given the shorter service life of paint. If you are interested in plastering your pool but would like to delay the renovation for a few years then you might want to consider painting with a low cost water based pool paint. Less durable, less expensive and easier to apply (and remove) than epoxy or rubber paints, water based pool paints are a decent option if you need to get a few more seasons out of your pool. Since the paint is lighter duty and water based it can be removed with a 3500+ PSI pressure washer as opposed to other forms of pool paint which require sandblasting to remove. If you would like more information on this painting process you can read this article on how to paint a concrete pool. A short part 2 to this concrete pool structural leak video can be found here.

In wall steps - Vinyl liner pools that have a set of in wall steps that is attached with a flange and gasket system are one of the most likely sources of a structural leak in a vinyl pool. Where a return fitting has 4 compression screws, and a skimmer can have between 8 to 16 screws, a set of in wall steps will normally have more than 50 screws in the flange. A really wide set of steps could have even twice that many screws and this increases the chances that you will develop a leak in your pool considerably. As with other compression flanges and gaskets it is critically important that each and every screw is installed and is tight. Any one screw that is stripped, spinning or missing, will almost certainly be causing a leak. For novice liner installers a set of in wall steps can be challenging to install correctly. This increases the chances of a set of steps developing a leak more so than other flanges in your pool and if you suspect that your steps might be a problem then you should try to dye test them as slowly and carefully as possible. Pay extra attention to the bottom two corners of the flange as this is an area that is likely to become damaged from the liner stretching. Remove the beauty caps so you can see the installation of the screws to see if there are any missing, or if there are mismatching screws. Ideally you want to see everything looking uniform but often you will find different screws, oversized screws or new holes that have been added to deal with previous problems. If you see evidence that your steps have been altered at some point then you should scrutinize the step flange even closer.


Water Level As A Leak Indicator

If you are this far into this leak detection guide but are still struggling to find the cause for your leak then another tip is to watch the water level in the pool. This is especially useful for if you have a large leak with a high rate of water loss. If you were to let the pool continue to leak does the water level stop at any point or does it continue to drop? Since you should not drain most pools you do not want to just let the water level drop indefinitely as this could cause damage. It might however be worthwhile to let the water level drop on its own and see if it stops at any particular point. While this may not be a good idea for all pools, since most likely the water will turn green while you have the pool shut down for an extended period, the water level can still be a strong indicator as to the location of a leak. If you have a pool that leaks very fast (a few inches per day) then I would try this method. For slower leaks I do not think this will be as effective.

There are times where the pool will sit dormant, such as the winter season, where the water level might drop without you being aware of it. If this happens you might take the cover off of your pool in the spring to discover that much of the water has drained out of your pool. If this is the situation that you have then the point at which the water stops dropping will be a huge indicator as to the leak location. If the water drops until it reaches the bottom of the skimmer mouth then you most likely have a skimmer leak. If the water stops half way up the return port then this indicates a leak in the return lines somewhere. Same with the light or any other peripheral items in your pool. If the water drains completely out of your pool then this is a clear indication that the main drain is suspect. If you have a structural leak such as a hole in your vinyl liner or a crack in your concrete if you have a concrete pool, then inspect the pool carefully along the water level and you will likely find the problem. While letting your pool drain until it stops it not something you can do in most cases, on the rare occasion where you can let the pool find its own water level you will most likely also find the origin of the leak.





How Fast Does Your Pool Lose Water?

Continuing with the diagnosis of your pool leak you should start to monitor the rate of water loss in your pool. The rate of water loss is a good indicator for what might be causing the leak. Specifically, if you are able to monitor the rate of water loss closely enough you can begin to make assumptions about the leak. The best way to monitor the rate of water loss in your pool is to mark the water level on the face of the pool skimmer with a pencil. A small tab of electrical tape can also work however the pencil allows for more detailed marks.

What you hope to discover by monitoring your water loss is the possibility that external factors are affecting how much water you are losing. What you might discover is that the pool loses water only on certain days. An example of this could be that swimmers in the pool are causing more splash out than you realized. You would probably only notice this if you were watching and marking the rate of water loss on your skimmer on a daily basis. Another example might be that your filter is leaking water through the backwash line periodically. Basically you are looking for any signs of abnormal rates of water loss. In theory if you have a leak in your pool then you should be losing water at more or less a constant rate. It is important to note that pool leaks can be elusive and you should not put too much emphasis on one specific symptom of the leak. Gather as much information as you can and you will have a much better chance of tracing the leak back to the source.

If you have a suspected leak in your pool then one of the first tests that you should conduct is simply to monitor the rate of water loss for 24 hours as the pool operates normally. The fill the pool back up to the same level that you started at but this time turn off your pump for 24 hours. Does the rate of water loss change depending on whether the pump is on or not? While this is not a definitive answer to the leak location it is certainly a big symptom that you want to take note of. If the rate of water loss in the pool does not change regardless of the pump condition then this would make me lean towards a structural leak in the pool. If the pump being on or off changes the rate of water loss then this is a very strong indicator that you have a leak somewhere in the plumbing system.


Leaks In Pool Plumbing

If you have completed a hydrostatic test for your pool and you discovered that the pool stopped losing water once you plugged the skimmer and return lines then you can be reasonably sure that the leak is somewhere in your plumbing system and not within the main body of the pool. Along the same lines if you monitored the rate of water loss in the pool and noticed that the pool stops losing water (or loses less water) once you turn off the pump then this is also an indicator that the leak is somewhere within the plumbing system. If you have determined that the leak is somewhere in your plumbing system then you can proceed directly to a pressure test of the entire system. In the event that you want to (or need to) narrow down where the leak is before you do a pressure test there is some basic testing that you can do. If you only have three pipes in your entire pool system then proceeding straight to a pressure test might make sense. If you have a pool system with 20, 30 or 50 pipes then just knowing that the leak is in the plumbing system is not good enough. A pressure test is something that only skilled trades people should do since there is inherent danger in pressurizing plumbing lines. Hiring a pool company to pressure test 50 pipes is going to cost a small fortune so you can try to narrow down the leak location further. You need to run the pool for 24 hours with the pump running and monitor how much water you lose. Then refill the pool and go 24 hours with the pump off. From this test there are only four possible conclusions:


Pump off, pool loses no water - Very likely a pressure side leak in the return lines of the pool. If I were inspecting a pool that stopped losing water once you turn the pump off I am inclined to think that the pressure generated by the pump is exacerbating a crack somewhere on the pressure side of the system. I would also make sure to look at the waste line on the filter to make sure that water is not escaping the system through a faulty multiport valve on a sand filter. I would not discount the potential for a leak in the suction side plumbing however suction leaks can often slow down when under vacuum from the pump.

Pump off, pool loses some water - Possible suction side leak or broken pipe on the return side. Does the pool lose more water with the pump on but still has water loss in both conditions? If that were the case I would be inclined to think there is a broken pipe on the pressure side that leaks all the time but when the pump is on the leak is made worse. If you have the reverse situation in that your pool loses water whether the pump is on or not, but it appears that you actually lose more water when the pump is off then this would point towards a leak somewhere in the suction line of the pool. Does your pump struggle to prime or does it run with air visible in the pump chamber? These would also point towards a suction side leak.

Pump on, pool loses no water - If the pool loses little or no water when the pump is running but you note an increase in water loss when you turn the pump off then this would most likely indicate a leak somewhere on the suction line of the pool. When under vacuum from the running pump the water is not inclined to escape the system, but once the pump turns off the water begins to gravity drain out of a crack in a pipe or fitting.

Pump on, pool loses some water - If your pool loses water when the pump is on but stops leaking when you turn the pump off then this would most likely indicate a small crack somewhere in the return lines for the pool that gets worse when the pump is pressurizing the line. If your situation is that the pool leaks when the pump is on, and still leaks when the pump is turned off then the rate of the water loss is the big question. Does the pool leak more with the pump running or more with the pump turned off. More water loss when the pump is running points towards a pressure side leak where more water loss when the pump is off points towards a suction side leak.


By examining the unique characteristics of how your pool leaks you will be able to draw reasonable conclusions that allow you to focus your search on specific areas of the pool. At some point, without the presence of any additional factors such as visible damage to the skimmer or sunken / cracked pool decks, you will need to proceed to pressure test the pool plumbing system. A pressure test will be the only definitive way to isolate the leaking pipe and allow you to find the exact leak location.


How Do Pools Tend To Break

Understanding how swimming pools tend to break is one of the best tools you can have when trying to locate a leak. This is where an experienced swimming pool technician will have a distinct advantage over a pool owner trying to find a leak in their pool. There is no replacement for experience when it comes to being able to solve complicated problems by observation and interpreting the results of your tests. While you may not be able to have the benefit of years of leak detection experience you can at least be aware of some of the most common ways that swimming pools tend to break.

Return lines - The return lines of the pool are one of the most common parts of the plumbing system to develop a leak. When you attach a return pipe to the wall of the pool you are supposed to attach a 90 degree elbow and turn the pipe straight down directly after the return flange. By turning the pipe downwards immediately you relieve stress on the return fitting connection. In the event that a pipe is taken straight out the back of a return fitting, even by a small amount, the settling of the fill around the pool will cause the pipe to sink slightly. Even a slight settling on the pipe will put a great deal of stress on the connection point on the wall of the pool. The pool wall has zero give and the pipe has no choice but to move with the settling ground. The weak point will eventually crack right where the pipe meets the return fitting on the backside of the pool wall. A failed glue joint, dry fit fitting, or pipe fracture from freezing are all possible and can happen anywhere within the return line. Failures where the return pipe meets the pool wall however are more common than every other return line failure combined.

Skimmer lines - The skimmer line is most likely to develop a leak directly where it connects to the bottom of the skimmer itself. This area is prone to leaks due to the transition fitting between the pipe and the skimmer itself. Some skimmers use threaded connection points and some use a glued slip connection. Many glue style skimmers are made from ABS and a transition glue needs to be used to get a secure connection between the two materials. Using a PVC glue where a transition glue should have been used is a very likely place to develop a leak. If the skimmer uses a threaded connection then using the correct thread sealant is important. Teflon tape is the best material for making a permanent threaded connection to the underside of the skimmer. PVC glue is another good choice if both the skimmer as well as the pipe being used are PVC. In the event that a common thread sealant from the plumbing industry is used, pipe dope, there is the possibility that a crack can develop over time. Petroleum based thread sealants like pipe dope expand over time which is great for a secure seal on metal pipe systems. The relative weakness of the PVC systems used on swimming pools are not strong enough to withstand the expansion of the pipe dope and cracking of the connection on the underside of the skimmer can happen. In the event that water is able to become trapped in the skimmer line over the winter (in cold climate areas) then it is likely that the pipe directly below the skimmer will sustain damage. In some cases a very careful examination of the pipe below the skimmer using a flashlight will reveal cracks in the pipe directly where is exits the bottom of the skimmer. Unfortunately leaks in skimmers can be fairly difficult to deal with as access to the underside of the skimmer is obviously limited. For more information on how skimmers are installed on both concrete and vinyl liner pools, and how to replace them, you can read this article on how to replace a pool skimmer.

Plumbing materials - If the plumbing lines that were used to install your swimming pool are known to be problematic then this would be a strong indicator towards a leak in the plumbing system. Schedule 40 PVC pipe, either flexible or rigid, is the industry standard minimum for pool installations. Using HDPE (high density polyethylene) or LDPE (low density polyethylene) was common in previous years and is recognizable due to the barbed fittings and stainless steel clamps used to make fitting connections. While poly pipe is suitable for swimming pool installations it is an antiquated process for the most part with most current day installers preferring PVC systems. The pipe connection points on poly pipe are susceptible to failure over time. A failing pipe clamp will start by leaking slowly, most likely too slow for you notice at first, but will increase over time. Eventually a pipe clamp can fail completely which will allow even more water loss from this location. The quality of a poly pipe connection is only as good as the person making the connection. Using heat on the pipe, or a black tar product, or both, are good ways to increase the quality of a poly pipe connection. Using a ratchet as opposed to a screwdriver to tighten the clamp is important to ensure a leak free seal. High quality stainless steel clamps are also important as low quality stainless steel will corrode when buried or exposed to chlorinated water. While there are many other types of plumbing materials used on swimming pools PVC and poly are the only two accepted materials used in current day installations. For more detailed information on the plumbing materials used in swimming pools you can read this article on pool equipment installation.


Copper pipe, ABS pipe, schedule 20 PVC or galvanized steel pipes should all be avoided for use in swimming pools. If you have any of these materials used on your swimming pool then the chances of you having one, or many, leaks in your plumbing system go up dramatically. In my experience I would tend to avoid extensive troubleshooting on plumbing systems using any of these materials. If you have these materials on your plumbing system then they are a guaranteed failure just waiting to happen. Spending money on labor finding leaks in a faulty plumbing system is not a good investment of time and money in my mind. If you have inferior plumbing materials then you may want to explore the potential for replacing all of your plumbing lines to something more reliable. The benefit of this approach is that you do not waste any money chasing a leak and instead replace the entire plumbing system right away. While this is going to be a costly project, and not something that you will have the option to do on every pool, it is worthwhile to consider doing anytime you discover a leak in the plumbing system of your pool. Replacing the plumbing lines completely may end up being the lesser of two evils and a more efficient allocation of your time and money.


Swimming Pool Pressure Testing

Pressure testing the plumbing system of your pool is the only way to definitively identify and isolate leaks with this part of your pool. Up until this point all of the tests we have been discussing are something that the average pool owner is able to do. Pressure testing is not the same. Pressure testing is a potentially dangerous process and not something that inexperienced people should attempt to do. This is not a generic warning that you should interpret as a challenge to take this on yourself - pressure testing is dangerous enough to kill you if something goes wrong. Unless you have specific experience in working with pressure vessels then you should not attempt to pressure test your plumbing system. Even a low pressure test at a few PSI is dangerous if you do not have enough respect for how powerful a pressurized pipe is. Most pressure tests for pool equipment for leak detection can be completed at around 10 - 20 PSI. 10 - 20 PSI is enough pressure to blow a hole clean through your abdomen if you had a pressure tester break loose while the line is pressurized.


Water testing - One method of pressure testing is to charge the entire plumbing line with water. This is less dangerous than a pipe charged to the same PSI but filled with air. Since water can not compress the same way that air does a water test is easier to do with a small compressor. Typically you will have a better ability to hear a leak when you are water testing as opposed to air testing. With a custom pressure tester you can actually use the water pressure from your home to pressurize your pool pipes since the average home has between a 20-30 PSI water supply. Simply use a garden hose to connect to your pressure tester instead of a compressor line.

Air testing - In some cases an air test may be preferential to water testing the plumbing lines. When you pressurize a line with air the PSI reading on the gage will tend to fluctuate so reading exact measurements is slightly more difficult than with a water test. Air tests are good for return line leaks to help you identify if the pipe is broken at the return fitting as the air bubbles will be able to be seen and heard in many cases. Air tests are also good to help make sure that your plugs are not leaking. Plugs in the returns and in the skimmer will be very obvious if they are leaking as they will have bubbles coming out of them.


The process of pressure testing a pool is simply to seal the pipes from one end while pressurizing the pipe from the other. A closed loop plumbing system should be able to hold pressure indefinitely so any recorded drop in pressure indicates a leak somewhere. It is important that you test your plugs and pressure tester itself to make sure that you are not invalidating the test results with your equipment. Using a spray bottle with soapy water is the easiest way to double check that your equipment is not leaking.



If you do not have a pressure tester in your tool kit then this style is by far one of the least expensive ways you can make a pressure tester. This system has a 2 inch tee fitting that you would glue a spigot adapter into one end. You would then glue the bushing into the small port on the top of the tee. The pressure gage will thread into the bushing. Now all you need to do is connect a garden hose to the spigot and you have a functional pressure tester for your pool. While you have a pressure tester capable of testing your pool system you will still need to figure out how to connect the tester into your system. With this style of pressure tester you will need to cut into the plumbing system and glue the tee fitting into place. A better idea would be to buy a 2 inch pipe nipple and glue this into the tee. Now you can thread your tester into a 2 inch female thread. Order a handful of 2 inch female adapters which you can glue into your system and thread your pressure tester into.


How To Pressure Test A Pool


Swimming pool systems operate between 0 - 30 PSI. Anything over 30 PSI is considered too high for a plumbing system and anything over 50 PSI is enough for failures of pool equipment to happen. PVC pipes when properly primed and glued are capable of pressures up to 198 PSI for 1.5 inch pipe and 166 PSI for 2 inch pipe. These numbers represent the safe operating pressures for schedule 40 PVC pipe. The burst pressure for PVC pipe is over 1000 PSI so pool pipes are more capable than many people assume. For this reason when a new pool is installed the pressure test should be conducted at pressures greater than the maximum operating pressure that the system will experience. This means for new pool installation using PVC pipe the pipes should all be tested to greater than 50 PSI. Most pool installers do not do this. Most pool installers will pressurize a pipe to anywhere from 5 to 15 PSI however this is not sufficient to identify all leaks in a plumbing system. Some leaks may not manifest themselves until you are at or above 30 PSI. For the purposes of existing swimming pool systems a pressure test of 30 to 50 PSI or higher would be way overkill and may actually contribute to breaking the plumbing system further. If you have a plumbing system that is nearing the end of its service life then this means a pressure test may be the last straw and cause failures in the system in areas that were weakened but previously not leaking. For the purposes of trying to diagnose a leak in an existing pool plumbing system you should only need to pressurize the system to a few PSI to identify which pipes are leaking.


There are many different ways that you can make or buy a pressure tester for your pool equipment. Professional leak detection kits can cost many of hundreds of dollars but a simple pressure tester can be made using inexpensive parts from your local hardware store. The pressure tester shown above is just an inexpensive one that you can order online. It will work for testing a plumbing system but it does require cutting into the system and is not the most convenient method to pressure test a system. While this is a very cost effective way to get the job done the tester itself is bulky and inconvenient to use compared to other higher quality testing equipment. My preferred method is to build my own pressure testers using brass pipe and threaded fittings. I use a 1/2" threaded brass nipple as my connection point to the pool equipment. You can glue in a 1/2" threaded female adapter that you can thread the tester into or you can also drill and tap a 1/2" thread into the existing system which you simply plug with a 1/2" PVC threaded plug once you are finished with the test. The tester itself needs to have a tee fitting and a reducer bushing so you can install a pressure gauge as well as a valve to regulate the pressure in the system. If you are doing an air test then you will want to have a quick connect nipple for a compressor line. If you prefer to water test then you simply add a garden hose adapter that you connect your garden hose to for water pressure. For more advanced leak testing ability you can have multiple valves with both water and air connection points.


Safety concerns for pressure testing - This pressure testing information is intended to increase your understanding of swimming pool industry standards for pressure testing. If you want to pressure test your own pool then you need to be capable and experienced in working with dangerous processes like pressurizing a plumbing system. When conducted properly a pressure test is a reasonably safe process. When pressure testing it is critically important to close the area to other people (including the pool area) and wear safety gear such as safety glasses, a full face shield, hearing protection and heavy clothing. You also must tie off your pressure testing equipment. In the event that you have a failure of some kind you need to be sure that the tester can not shoot out like a missile and hit you. When I am pressure testing I wear all of the equipment described above and I tie off my testing equipment twice with steel tie wire for redundant protection against a blowout. The pressure testing plugs that you use must also be tied to prevent them from exploding out in the event that they become displaced during the test. A pressure test of 10 - 20 PSI is enough pressure to shoot a pressure testing plug well over a hundred feet in the air. For the relatively low cost of a pressure test consider hiring a professional pressure testing company instead of risking your own health and safety. If you are 100% confident that you can do a pressure test safely then the actual process is not specifically difficult. The real difficulty is actually finding the leak once you have identified which pipe it is in.

Once you have determined which pipe in your pool is leaking you can attempt to find the exact location of the leak by listening for the sound of water (or air) escaping the system while you have the pipe under pressure. If you would like more detailed information about industry standards for pressurde testing, as well as more information on how you can build your own pressure testers, then read this article about pool pressure testing.


Plumbing Leak Detection

A pool plumbing line should be able to hold pressure indefinitely without any drop. You should be able to leave a pipe under pressure for 24 hours and note zero drop in pressure. In the real world this is usually not the case. It is very common for plumbing lines to have small leaks that do not amount to a noticeable problem under normal pool operating conditions. When monitored under pressure these lines will lose a very small amount of pressure over time. To provide a relative context if I am searching for a leak I would be expecting to see a drop in pressure within 60 seconds of charging the line. A total break in a pipe would not be able to build pressure at all. If you have a line that builds and holds zero pressure then an air test is not likely going to help you to locate the leak point. If you were to flood the pipe with water however the area surrounding the broken pipe will fill with water and you should have a greater chance of being able to hear the problem area with your listening device. A completely severed line is a very major leak and you would probably already know that you are looking for something like this due to the extreme rate of water loss you would have while operating a pool with a broken line. Most pool leaks will be from a crack in the pipe or in a fitting. These cracks will lose water when under pressure and less so when the pump is turned off. For a small crack in a plumbing line I would expect to drop from 10 PSI to 5 PSI in one to five minutes. A good process to follow would be to air test the pipes in question. If you are able to identify the pipe but not able to hear the leak by ear or with a listening device then you can flood the line with water. As you inundate with water the remaining air in the pipe will be forced out through the crack. This will produce a gurgling effect and can aid you in hearing the leak location.




If you hire a professional leak detection company to find your leak then they will probably show up with a system very similar to this leak detection kit by Fisher Labs. At over a few thousand dollars in price this is not something that the average pool owner would, or should, own. Swimming pool companies looking to offer leak detection services or pool builders dealing with elusive leak problems should own a kit like this one. Using a system like this effectively to find a leak in a pool does require practice. In most cases using leak detection equipment like this will require training in order to use it effectively. Simply having expensive equipment does not automatically mean that you are going to pinpoint your leak location. If you are a professional looking to improve your ability to locate pool leaks then you should also research Anderson Manufacturing who have a ton of specialized leak detection equipment. You should also look at Fisher Labs as well as Leaktronics who also make a professional leak detection kit.


Many pool companies have purchased equipment like this and still fail to be able to locate leaks effectively. There is a learning curve to working with electronic leak detection equipment as you have to learn how to calibrate the device for optimal results. You also must learn how to hear a leak through the background noise and static that is part of using listening equipment like this. Most leak detection manufacturers offer training materials and courses intended to help professionals improve their ability to use their equipment and find leaks effectively. The world of professional leak detection goes very deep and the equipment costs well over a few thousand dollars. So what did people use before sensitive electronic listening devices came along?




A stethoscope has been the traditional tool for hearing underground pool leaks for decades. Similar to the more expensive electronic equipment, using a tool like this to pinpoint a leak location takes patience and practice. All leaks will present themselves differently depending on the size of the leak, the soil conditions, the depth of the pipe, the pressure of the system and orientation of the break in the pipe. Using a stethoscope enhances your ability to hear subtle noises and once you learn to differentiate a leak noise from the background static noise then you might be able to use one to find your pool leak. While any stethoscope might work, even a toy stethoscope, if you are serious about finding your leak and you want a decent tool to help you listen for it then consider the Littmann Master Classic II Stethoscope which has a sealed, water proof chest piece which is extremely useful if you are using this to locate a leak around a swimming pool. Since this is a veterinary stethoscope it also has a longer reach than traditional stethoscopes which is extremely useful.


Locating Pool Leaks

Locating a leak in a swimming pool takes more than just specialized equipment. Understanding how swimming pools are built and how they tend to break is a huge component of successful leak detection. Even with listening devices it can be very difficult to locate a leak. Having experience allows you to know where you should be focusing your attention and will also allow you to pick up on subtle symptoms that might escape the average pool owner.

Often is the case that swimming pools can have multiple leak locations or intermittent symptoms which vastly increases the difficulty in finding the leak. Even if you manage to find a leak and make a repair you may discover another leak present in the system. When I approach a leaking swimming pool plumbing system I am always mentally preparing to pull the plug on the leak detection process and proceed into a plumbing line replacement renovation project. If I feel there is a good chance that the leak can be found and repaired, and I suspect only a single leak location, then I will attempt to locate and repair the leaks. If the plumbing system is installed incorrectly or installed with inferior plumbing materials then I usually will advise to invest in replacing the lines as opposed the repairing the old ones. While the thought of replacing your pool plumbing might be unpleasant the reality is that a leaking pool needs to be fixed and you could easily spend a lot of time and money chasing a leak only to discover that repair is not an option. If there are multiple holes or a systemic failure of some kind then all of the resources put into detection are lost and you must still foot the bill for a new pipe installation.

As you are going through the leak detection process on your pool be sure to keep comprehensive notes about the tests you do and the conclusions from them. Even if you end up unable to locate and repair the leak yourself, the information that you have gathered can help to fast track any professional leak seekers that you hire in the future. General observation, basic testing and an understanding of how any why pools develop leaks is your best defense against leaks in your swimming pool.





Swimming Pool Steve

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