Water loss from Your pool can only be from the re-circulation system or the structure.
You have to look for any obvious wet spots everywhere. In the yard or around the filter system.
Swimming Pool Re-circulation and Plumbing.
Your swimming pool is a bowl for water, the pump/filter system moves that water.
This system includes:
- Skimmers and suction ports below the surface.
- Hidden suction lines back to the pool.
Suction lines if leaking may not work at all or show air and/or mud in the pump.
- The pump that is pulling water from the pool.
The pump is both suction and pressure… at the lint trap and all in front of that is suction.
Just behind the lid at the discharge port it becomes pressure.
- The multi-port valve and filter that the water is pushed through.
- Then maybe a heating system, or a chemical feeder.
- Pressure return lines back to the pool.
At the multi port valve you have a pipe on the upper part of the filter and one on the lower.
One to the pump, one to waste, and one going back to the pool or next piece of pool equipment.
First see that water is not going down the waste line, find the end of it and look, if you can’t find it, cut the pipe to see if it leaks.
If it does that is good news, repair the valve and your leak may stop.
The return lines to the pool could be the source of a leak, there are more than a few ways to check them, the short quick way is a simple pressure test.
In order to check the pool before the pressure test, if the system is not too far away I have plugged the return lines and then run a temporary line to the system over the deck to the pool.
Using pipe or a good vacuum hose as a return.
If the water stays at the correct level, you may now know the problem, but where the leak is will be another story.