If your pool loses water when the pump is off, the leak is almost certainly in a part of the pool that is always in contact with water -- not in a pressurized line.
This is called a static leak. It happens at the natural water level regardless of whether the system is running. Common sources include the pool shell, skimmer, light niche, return fittings, main drain, spa bond beam, or suction-side plumbing that holds water when the pump is off.
A Useful Clue: Where Does It Stop?
If the water drops to a certain level and stops, that level is an important clue. If it stops at the light, the light niche or conduit may be leaking. If it stops at the skimmer mouth, the skimmer is a likely source. If it stops at a fitting or return, start there.
What LSL Looks At
- Pool shell and finish for cracks or separation
- Skimmer throat, body, and pipe connection
- Light niche and conduit
- Return fittings and main drain
- Spa bond beam and spillover
- Suction-side plumbing that drains back when pump is off
At Leak and Subsurface Locators, we evaluate the pool with the pump on and off because each state can reveal different things. Testing both gives us a more complete picture of where the water is going.
Free tools from Leak and Subsurface Locators:
Free Guide: Stop Guessing Pool Leaks → Free Evaporation Calculator → Free Leak Analyzer →