1. Turn off the automatic fill valve and place a bucket on a step where the bucket rim is at least a few inches above the water line.
2.Place a heavy weight in the bucket and add water until the water level inside the bucket is equal to the water level in the pool.
3.Leave the bucket and pool undisturbed for several hot days, and then compare the water level in the bucket to the water level in the pool. If the water level in the bucket is noticeably higher than the water level in the pool, you may be losing water to a leak. If this is the case, contact a pool leak detection specialist for further assistance.
Automatic Fill Valves
Some pools and spas may have an automatic pool fill valve allowing water to fill when the level is low. Similar to a toilet float these pool fill valves are a common leak culprit.
To determine if a leak is present, visually inspect the float and arm and determine if the water continues to fill even after the water level in the pool is at its normal height. If the float does not rise and stop water flow this may indicate a leak.