How To Drain A Swimming Pool
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If you are looking for information about how to drain a swimming pool it is critically important that you first understand that some pools should not ever be drained. Draining a swimming pool incorrectly, or draining the wrong kind of pool, can result in anywhere from minor damage all the way up to catastrophic destruction of the entire pool. You would be well advised to take a few minutes and review the information contained in this article about how to (and how to not) drain a pool.
The most important thing that you need to know before you even think about pumping down the water in your pool is simply what kind of pool do you have? There are a few different kinds of swimming pools, and a few slightly less common hybrid versions. If you are not 100% sure what kind of pool you have, you can review this article about different types of swimming pools. The main types of swimming pools are concrete, vinyl liner, fiberglass and hybrid. The answer to how to drain your pool is complicated, with quite a few potential variables, and a whole lot of money on the line...it can not be stressed enough that swimming pool industry professionals exist for a reason. Even for a professional, draining a pool is risky business and sometimes accidents will happen. You assume this risk any time you remove the water from an inground pool. It could be that there is even a hidden deficiency in the pool, or a pool was not built correctly decades ago, and draining can cause anything from small cosmetic problems, all the way up to huge un-fixable structural issues. This is the risk you take when you drain a pool. Industry professionals have experience to help us safely drain pools and insurance to help us if the worst case scenario happens.
Do not drain your pool. Just don't. Something might break. It is not worth it. If you do anyway, consider yourself warned!
With that disclaimer aside, and knowing that you will probably listen to all the good advice I have other than telling you not to drain the pool in the first place, if I were to drain a pool, this is how I would do it. I would start by being prepared, both time wise and financially, to take on pretty much any, and every, pool repair you can imagine. You might think that is ridiculous, but if you hire a pool professional this is what they are ready and prepared for.
As a pool owner you can very quickly get in over your head when you start to drain your pool. But what does that mean? What, specifically, is going to happen if you pump down your pool? The answer to that will depend largely on the type of pool that you have and how you go about draining it.
Vinyl Liner Pools - Vinyl liner swimming pools should maintain enough water level to cover the floor of the shallow end completely. In general terms 12" of water covering the floor in the shallow end is a good minimum. But what if you have a repair that needs you to pump the water level lower. If it is a game of inches, I would even go a little less than 12" of water, perhaps as low as four to six inches of water in the shallow end in order to facilitate a repair. I would only do this however if the floor of the pool and the site conditions looked good. Lowering the water level below this safe threshold requires installation of liner vacuums to hold the liner in place until the water level can be raised above the shallow end floor again.
Concrete Pools - Concrete pool shells are hydrostatically balanced in the ground via a relief valve that is installed in the floor of the pool. This allows water from under the pool to come through the floor and into the pool shell should the pressure from below the pool be greater than the pressure of the water pushing down from inside the pool. As you remove the water from the pool, if there is ground water surrounding the shell, it will put pressure on the pool to lift. In extreme cases this can cause the entire pool to float, or "pop", out of the ground. Draining a concrete pool is not as simple as just "do these three things". There are a lot of factors such as time of year, recent weather and short term weather forecast, and current ground water conditions around the pool that must be considered.
Fiberglass Pools - Fiberglass pools are the same as concrete pools in that a fiberglass pool is hydrostatically balanced in the ground. A hydrostatic relief valve should be installed in the floor main drains to allow the pool to balance the hydrostatic pressure of the ground water surrounding the pool. This is even more important in a fiberglass pool than a concrete pool simply because a concrete pool weighs so much more than a fiberglass pool, it is easier to experience a floating pool with a fiberglass pool than a concrete one under similar conditions. Additionally a fiberglass pool requires the force of the water in the pool to help stabilize horizontally in the ground, and bowing or flexing of the walls can happen when you drain a fiberglass pool.
Hybrid Pools - A hybrid pool has a water resistant concrete floor as well as panel wall segments which are seamed with a sealant. Draining a hybrid pool is most similar to draining a concrete pool however there is also concern for shifting or bowing wall segments when the pool is empty. The concern for this kind of problem with a hybrid pool is not just cosmetic. The water retentive abilities of a hybrid pool come from the wall panels being seamed perfectly together. If they shift, move or bow, you almost certainly will lose your water tight seal.
Any time you drain a swimming pool, any kind of swimming pool, the goal should be to have the pool empty for as little time as possible. Drain the pool, do the work that needs to be done, and fill the pool with water again as soon as possible. There are many people who leave their pool empty for extended periods of time, and doing so does not guarantee that the pool will be broken, but you would be absorbing an unnecessary amount of risk doing so.
When To Drain A Pool
The first part of draining a swimming pool that some pool owners do not know about is simply that you can not drain a pool any-old time you want. You need to pick your moments. The first thing that you need to consider is what has the weather been like lately? Has it been raining heavily for the past month? Or even the past few days? What does the next two weeks to one month look like for rainfall? If there has been a lot of rain recently, or you suspect there will be quite a bit of rain in the relatively near future, you may want to wait to drain your pool.
It can take a few days for water to travel through drainage systems and the ground water tables in your area can continue to rise even up to a week or more after heavy rains. Typically speaking you want to avoid times of year where there is predictably high levels of rain, or snow melting, which could elevate the water table around your pool. Long stretches of dry weather is the optimal time to drain a swimming pool. It is not a guarantee that there is no risk of your pool floating, but just one of the many steps that you can take to lessen the chances of encountering a problem when you remove the water from your pool.
Even if you have the best of intentions, sometimes draining your pool can reveal problems, or even cause problems, that you must attend to before filling the pool back up with water. What happens if you discover a problem (or make a problem) that requires a unique piece or part that is hard to find? Special order pool items can take weeks to arrive during busy times of year. Also you might find something that you are not sure what to do with, or worse, find something that for sure needs more experienced hands working on it than yours...will you be able to get a professional to come out and look at the problem in short order? Swimming pool companies get absolutely slammed in peak seasonal times so you may find yourself with your pool sitting empty while you wait for someone to come and look at it.
Where To Drain A Pool
The next most important consideration when it comes to draining your swimming pool, is where are you going to put all of that water? The answer to this question is complicated simply due to different regional areas having different accepted industry practices. Most commonly you will fall into one of three categories for where you should be draining your pool to:
Pump Water To The Street - In many populated areas where there are storm and sewer drains in the roads it is commonplace to pump the water to the street in front of your house. From there the water is whisked away by the same city infrastructure that deals with torrential downpours and melting of accumulated snow. If your local city code allows for discharging of pool water to the curb then this is the ideal (and often only) option for where to drain your pool water to. In some more populated areas environmental concerns have caused additional restrictions to be placed on discharging swimming pool water into city drainage systems. Some areas now require that the pool water be neutralized for both chlorine, and also pH neutral, before it can be discharged into city drainage systems. Also some areas have placed restrictions on discharging salt water pools to city drainage systems altogether. While chlorine can be neutralized in pool water before discharging, salt can not.
Pump Water Into Your House Drain - When there are local bylaws about discharging salt water pools to the street, it is generally recommended that you discharge the pool water into the sanitary drainage system for your home. While this does help to ensure that your pool water will be collected and treated instead of being fed directly back into the local ecosystem, this means that you need to drain your pool into your house. This is certain to result in people flooding their homes if the drainage system of the home can not keep up with the flow of water. Since it takes so long for a modestly sized pump to drain a pool this means that the pool will be draining while unmonitored for at least some of the draining process. In addition to this you likely will be paying for the disposal of this water as part of your monthly utilities bill. This, if made commonplace, would increase the cost to pool owners substantially any time you need to lower the water level of your pool.
Pump Water Onto Your Property - With restrictions about where you can discharge your pool water becoming more common, it will also become more common for pool owners to start draining their pools onto their own property somewhere. While this can be a valid method of draining your pool, and the chemicals in the water will not likely cause any damage to your property, there is specific concern for the local water table around your pool if you discharge the water upstream, or too close, to the pool. I can not count the amount of times I have found pool owners draining their pool onto the grass directly adjacent to the pool. If you wanted to set up a laboratory experiment to try to get a pool to float up out of the ground, this is pretty much exactly what you would try to do. If you are going to pump out your pool onto your property then you need to have a reasonably large property, and you need to pump as far away from the pool as possible.
There is also the potential to hire a water truck or water bladder service depending on where you live. Some areas where water use is strictly regulated it can make financial sense to hire a company that will remove the water from the pool and store it in a bladder on site. Unfortunately this would not apply to situations where the water will need to sit for anything longer than a day or so, and would obviously add considerable expense to the process. Along the same lines, you can also pay to have your water trucked away and disposed of, but again this is cost prohibitive and would only apply to areas where there simply are no other options for where to drain your pool to.
How To Drain A Concrete (Or Fiberglass) Pool
Every attempt should be made, while draining your pool, to control the ground water table surrounding the pool. The higher the water level is, the greater the pressure it will put on the pool to lift up out of the ground. Ideally, all swimming pools should have a well pit with a submersible sump pump installed directly adjacent to the pool, and it should extend down at least one foot below the deep end floor of the pool. Having the ability to run a well point pump continuously during the period where the pool is empty not only makes it a much safer process, but it also makes working on the pool much easier also. Many pool processes require the pool to be completely dry, and having ground water accumulate in the pool can hamper this. A well point installed below the depth of the floor of the pool will allow you to limit, if not completely prevent any ground water from making it into the pool.
Without a well point or sump pit installed on your pool then you will have very limited options for how to deal with the ground water table around your pool. All concrete and fiberglass swimming pools should have a hydrostatic relief valve installed in the main drain. This is a one way spring loaded valve, and when you drain a concrete or a fiberglass pool you should remove the HRV until the pool is ready to be filled again. When you fill the pool be sure to replace the HRV with a new valve. The HRV is a mechanical device, a stainless steel spring and PVC flapper, and the spring can corrode and fail over time. Since they are located in such an unserviceable location, you should replace it any time that you have the opportunity to do so.
By removing the HRV you now effectively have a 1.5" hole in the floor of your pool. This will allow ground water to start to fill into your pool. If you let the ground water flow unrestricted, and do not pump out the water from the pool, you would eventually be able to see the level of ground water around your pool. Whatever the water level stops at inside the pool, this is where the water level is on the outside of the pool walls. It is very common to have a submersible pump running in the bottom of a pool throughout the time that the pool is empty. This helps to be able to work on the pool with minimal risk for any damage as a result of hydrostatic pressure lifting the pool. So how do you stop the water from coming in when you need to paint the pool or plaster the interior surface where it needs to be dry inside the pool? You can either plug the HRV port with a rubber winterizing plug temporarily while you work, or you can install a standpipe if you are worried about changing water level conditions. A standpipe is just a piece of straight pipe that comes up out of the same hole that the HRV valve was installed in. By threading a male adapter into this hole you can stand a piece of rigid PVC straight up out of the main drain. Cut the PVC to 12" to 18" higher than the current water table level and leave the pipe open at this height. If the water level around the pool rises more than 12" to 18" then the water will be able to equalize into the pool at this height. If you had to leave a pool drained and unmonitored for an extended period this would be a good precautionary procedure to take.
Some pools, especially older ones, may not have an HRV or the one that was there might be permanently stuck in place. This is not a very good situation to have and an example of when hiring an industry professional can really be worth the money. A threaded connection in the very bottom of your pool that gets touched once every 10 to 20 years can certainly pose some problems to anyone trying to remove it. You can break the valve, or worse, crack the main drain itself...and then what are you going to do? If you start to work on an HRV in your main drain you need to be exceedingly careful about what you are doing as any problems that can develop will all be big problems. So much so that I would rather an inexperienced person simply leave an old HRV in place, instead of trying to remove an ancient HRV and replace it as preventative maintenance.
Again, dealing with a worst case scenario, how would you equalize a pool where there is no HRV, no well point, or any way to control the ground water around the pool? These are the cases where you hear of people drilling holes in the floor of the pool. I would never advise a pool owner to do such a thing. Even professionally, if there is risk for ground water pressure I am not inclined to start drilling holes through the floor of the pool. If I do feel that something need to be done to equalize the pool with the ground water around it, I will drill a single 1/2" hole through the shell of the pool floor. If there is water around the pool you would certainly know it at this point. I have seen water geizers that shoot well over my head when you drill through the floor of a pool like this. Instead of drilling multiple holes, I prefer to drill only the one and leave the pool overnight to slowly fill with ground water. By morning the pool water level should now have stabilized. I would then pump down the pool and continue to pump with a submersible pump non-stop for 24-48 hours depending on how high the water level was in the pool and whether the rate of ground water coming into the pool has slowed at all.
With a submersible pump running I break open a floor area of the pool that is slightly above the height that the submersible pump is able to keep the water level. This will help to be able to concrete a new main drain into the floor of the pool without ground water causing it to compromise the concrete patch work. Since this new main drain is not connected to any plumbing system you do not need to install two as per the VGBA for dual main drain suction points, as there is no suction. With a new main drain installed in the floor you can now have the ability to install a new hydrostatic relief valve. To repair the floor of the pool where I drilled a 1/2" hole, I use a wine cork to stuff down into the hole I drilled and stop the flow of water. Once you have stopped the flow of water here you can clean out the rest of the hole and fill with hydraulic "water stop" cement. Be sure to run the submersible pump in the new main drain you installed until you have the floor patch completely finished.
Please note - The information above is not intended so that the average pool owner should start drilling holes in the floor of their pool to relieve suspected hydraulic pressure. If anything this information is intended to help pool owners understand the difficult nature of working on pools, and the lengths that you need to go to in order to minimize the potential for problems that result from hydrostatic pressure. Even when all of the correct steps are taken in order to drain a pool safely, it is still possible that the unexpected happens. If you are not ready to assume this risk then you should not drain your pool - it's as simple as that. All too many pool owners have learned the hard way that blindly draining their pool without taking these considerations into mind can have disastrous consequences.
Fiberglass pools are more likely to have a functional HRV than concrete pools simply because there are so many 50 year old concrete pools still in operation, and vastly less so, fiberglass pools of similar age. In most cases this means that you can just remove the HRV from your fiberglass pool main drain, and you should not need to worry about drilling holes in your pool. Fiberglass pools can not resist the forces of the ground pushing against them as well as concrete pools or even vinyl liner pools. Most often fiberglass pools are backfilled around the outside at the same time that the water level is raised in the pool. This helps to make sure that the shell does not twist or distort shape in the ground. If you want to drain a fiberglass pool you should speak with a pool professional first, or at the very least consult with the manufacturer of your pool shell to verify draining procedures.
How To Drain A Vinyl Liner Pool
Most of the information above relates specifically to concrete pools, and to a lesser extent, fiberglass pools. Vinyl liner pools on the other hand are a little bit different. Concrete pools and fiberglass pools, and even hybrid style pools all have the same feature which is that the pool shell itself is an integral part of the water proofing (water resisting) process. A vinyl liner pool has a structural shell which is specifically not water proof, with the water proof barrier coming from the vinyl liner over the interior surface of the pool.
You typically only drain a vinyl liner pool in order to replace the liner. It is very uncommon to drain a vinyl liner pool lower than about 12" of water covering the shallow end for general service or repair. Even extremely dirty water in a vinyl liner pool is most often dealt with by partially draining and refilling versus draining completely. This is because the liner will shift as soon as the weight of the water is taken off the floor of the shallow end - and it does not go back once you add the water again. If the pool is to be drained lower than the shallow end, and you are not replacing the liner, then you need to install liner vacuums to hold the liner in place. These vacuums need to run continuously until the water level in the pool is back up and covering the floor of the shallow end.
Assuming that you are replacing the vinyl liner, at some point you need to actually drain the pool. Some pool technicians prefer to measure new liners with the pool full, and others prefer to drain the pool and remove the old liner in order to get more accurate dimensions for the new liner. Since it takes a few days, and sometimes a few weeks to make the new liner, it is somewhat normal to see vinyl pools sit empty for extended periods of time. While this is not a process without risk, there is less overall risk as compared to concrete or fiberglass pools since water can and will readily find its way into your empty vinyl pool. This is actually a function of the design and completely normal. While you can have a vinyl pool sit empty for a short period of time, it is possible that the pool walls can bow or shift, as well as the floor of the pool developing cracks from migrating water undermining the concrete. Ideally you want to leave your vinyl pool empty for as short a time as possible to limit your liability and the potential for damage to the pool. In most cases vinyl pools do not need HRV's installed since water can usually find multiple entry points into the pool through the non-structural floor of a vinyl pool, as well as between the joints between the wall segments and the start of the floor.
If you are looking for more information about how to care for your pool then start with this artice that covers all of the essential information for new pool owners. This will give you a good starting point for learning about your pool and even if you have owned your pool for a while there is still much to learn from this article. After that you can follow all of my swimming pool and hot tub tutorials and articles through my swimming pool blog.
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