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.