Why Is My Pool Losing Water? It May Not Be What You Fear




When a pool starts losing water it is not unreasonable to start panicking and imagine the thousands of dollars that you may need to spend to dig up pipework, replace the liner or do other major works.

All pools lose water and it is easy to jump to the conclusion that you must have a leak. But actually, the most likely reason for your pool losing water is through evaporation. A pool can lose much more water by evaporation than you might imagine, particularly at certain times of the year and when certain conditions exist.

For the first year or two I never had to top up my pool as it had an automated top up system. Then that system stopped working, so, until I fixed it, I needed to top the pool up with water from a hose pipe whenever it went down.

It certainly surprised me how quickly the water level dropped in my pool then. I was having to top it up twice a week so I began to think that there must be a leak which didn’t show up before due to it constantly being automatically topped up.

Topping up the pool due to evaporation
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So a friend explained the “bucket test” to me so I could prove whether I had a leak or not – and I was utterly convinced I had one I can tell you. I carried out the bucket test (see below for instructions) and to my amazement, and complete relief, it proved that I didn’t have a leak at all.

Reasons for a pool losing water

There a number of reasons why a pool might lose water which could be happening individually or in combination with each other.


It is incredible just how much water a pool can lose due to evaporation alone. The amount of water loss can vary quite dramatically depending on various factors such as wind, humidity, air temperature and water temperature.

This variability is one of the reasons that people often think that they must have a leak. They know that this month there is twice the water loss than there was last month so it must be a leak. But it may well be that last month the air temperature was low, the water was cooler and it was not very windy but this month it has been hot and humid with lots of wind, resulting in a higher rate of evaporation.

A normal pool evaporation rate can be as much as 0.25-0.5 inches per day (2-4 inches per week) due to evaporation alone. Obviously, if your pool is losing 10 inches a week then there must at least be other causes.

Bucket Test

The best way to check if your pool losing water due to evaporation is to carry out the “bucket test”. Read my full instructions on how to carry out the bucket test to find out more.

Basically, you put a bucket on a step in the pool (or on something to raise it up if you don’t have steps) so that a few inches of it is out of the water. Then fill it to an inch or so from the brim with water – ideally to the same level as the pool water outside. You then mark the water level of the pool on the outside of the bucket and of the water in the bucket on the inside.

Leave it for a few days (ideally) and then measure both the water loss inside and outside the bucket. If the levels have gone down by the same amount, or pretty close, then the water has been lost through evaporation. If the pool has lost significantly more then there is another problem.

If this test confirms that you are losing water due to evaporation you can reduce this. See the section below on how to reduce loss due to evaporation.


When you backwash a pool the water does not return to the pool but is expelled either to the drainage system or into your yard, so the water level will drop to some extent. However, as you generally only backwash for a few minutes this is unlikely to significantly affect the water level.

Vacuuming to waste

Just like backwashing, when you vacuum a pool to waste water does not return to the pool but instead is expelled. However, unlike backwashing, the process of vacuuming to waste takes significantly longer so a large drop in the pool’s water level will occur. I tend to lose about 4 inches of water every 10 minutes or so when I vacuum to waste.


Why Is My Pool Losing Water? It May Not Be What You Fear 1

This may seem like an unlikely reason (well impossible if you don’t have children using your pool of course) but if you have kids using the pool frequently it can have quite an effect on the water level.

Children tend to be forever getting in and out of a pool the running around dripping water as they go. Then they jump back, in splashing water as they go, particularly if they are fond of doing cannonballs.

The worst scenario – a leak

If you have eliminated all of the other possible causes then you will have to look at the unpleasant possibility that your pool may actually have a leak. I would suggest that you do this pretty quickly as the longer you leave it the worse it is likely to get, and probably more expensive it will be to repair.

Finding a pool leak

Pool leaks really fall into two categories, either external in the pipework or in the pool itself:

Leaks in the pool’s plumbing

Some of the pool’s plumbing will be underground, so less easy to check for leaks, but much of it is above ground (well all of it in an above ground pool of course). So first of all check all of this above ground plumbing for leaks. This includes:

  • the pipework from the skimmer/s to the pump
  • the pipework from the main drain to the pump
  • the pump itself
  • the multiport valve (if you have one)
  • the filter (sand, DE or cartridge)
  • if you have solar pool heating then check all of this. I had a small leak in one of my solar heating sheets on my roof last year.
  • as much of the pipework that returns to the pool as you can see

If there are any major leaks that are likely to significantly lower your pool water level then they should be easy to see. If there are then you are lucky as they will also be relatively easy to fix.

If everything is dry and leak-free then, sadly, things are not looking good for you.

To check to see if you have a leak in the plumbing underground then you can try to plug the skimmer, main drain and the pool returns so no water can get into them from the pool. If the pool level no longer drops at the same rate then it would indicate that the problem is probably in the underground plumbing system.

Leaks in the pool’s structure or fittings

If you have now reached the conclusion, through a process of elimination, that the leak must be in the pool structure itself then you have two options. You can try to detect the source of the leak yourself by using a pool leak detection kit (see below) or you can call in a pool professional.

Using a detection kit you need the water to be as still as possible so turn off your pool pump, shut any valves to the skimmers, pool drain etc and then leave it a while. Ideally, you also want there to be little or no wind that could move the water in the pool.

Leakmaster BLUEDYE8OZ Pool DYE Leak Detection, Blue

You then systematically go around the pool checking around all the fittings such as :

  • the skimmer housing
  • the skimmer pipe that goes from the skimmer to the pump and also the equalizer if you have two holes in the skimmer
  • the main drain – not an easy task as it is at the bottom of your pool
  • pool lights – check around the fitting
  • returns – check around the return jets
  • the pool itself, which could be a vinyl liner, tiles or fibreglass – the most common places are in the corners and where the sides meet the floor

Leakmaster BLUEDYE8OZ Pool DYE Leak Detection, Blue

These are basically a bottle of dye and a syringe applicator with a very fine nozzle so that a very thin line of dye is released when the plunger is depressed.

You gently put the syringe near somewhere in the pool you suspect could be leaking and release a small jet of dye. If the dye gets sucked into the fitting or wherever you are checking then there is a leak.

Pool leak detection kit available on Amazon

If you find a leak

Depending on where the leak is you may be able to get away with a simple fix by using specialist leak sealing products which you can use without the need to drain the pool. There are a few leak-sealing products available, none of which I can recommend (as fortunately, I haven’t had a leak yet) but they seem to have some good reviews.

If you find the pool losing water around a skimmer housing or a pool return you may be able to just lower the water level below that level then remove and reseal that particular fitting.

pool losing water - fixing a pool leak

You may not actually find a leak or, even if you do, for many leaks you will just have to bite the bullet and call in a pool repair professional. If you require a new liner or something like that then it could be quite expensive but it might not be as bad as you think. Obtain more than one estimate to make sure you are getting a good deal.

How to reduce loss by evaporation

One of the best ways of reducing the amount of water that your pool loses due to evaporation is to use a solar pool cover. Although the main function of solar pool covers is to retain heat, and also allow the pool water to heat up faster, they also significantly reduce water evaporation.

Actually, this is no surprise since one of the ways in which a pool loses heat is through the evaporation process.

You can also try a liquid pool cover which should also reduce the rate of evaporation.

Keeping the pool topped up automatically

If you do not have a built-in automatic pool leveler then you can easily install a Rola-Chem Sentry Automatic Pool Water Leveler which just attaches to a hose and tops the pool up whenever the level goes down. See the video below:

My top 3 pool cleaning tools

These are the pool cleaning tools I have found the most useful since I have had my pool.

Step and corner vacuum brush

This is a really useful tool for getting into the areas that a standard vacuum head simply cannot reach. Aquatix Pro Pool Step & Corner Vacuum Brush

Leaf rake net

If, like me, you get plenty of leaves at the bottom of your pool then a good leaf rake/net is a must. The Stargoods Pool Skimmer Net gets under the leaves easily.

Robotic pool cleaner

These are quite expensive and it was a number of years before I bit the bullet and bought one. I have never regretted it. The Dolphin Nautilus CC Plus is the most recommended pool cleaning robot on all of the pool forums. It not only cleans the bottom of the pool but also the sides and the waterline.

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