How to Test for a Leak in a Pool. Bucket Test…If you notice your pool-water level is decreasing faster than normal, you may have a leak. Follow these simple steps:
1. Fill a bucket with pool-water. Fill to about one inch from the top.
2. Place the bucket in the pool on the first or second step.
3. When the water stops moving up & down, and is very still, use a marker to mark the water level on the inside of the bucket.
4. Now mark the pool-water level on the outside of the bucket.
5. For the first 24 hours run the filter/pump continuously. DO NOT TURN IT OFF!!! After 24 hours, use a ruler to measure the water loss in the bucket and then in the pool. Measure down to 1/16 of an inch.And mark it for review later.
6. Next, turn the filter.pump off!
7. Make a new mark on the inside &outside of the bucket. NOW LEAVE THE PUMP OFF for the next 24 hours. DO NOT ALLOW THE PUMP TO TURN ON!!!!
8. After the 24hour off-period document the water loss again, in the bucket and in the pool(outside of the bucket). If they are the same-probably no leak.
9. If you lost more water in the pool than inside the bucket, it’s a good chance that you have a leak. (Remember, the bucket is the control and tells you how much evaporation exists.)  (Both the pool & bucket will evaporate the same amount.)
You will need to have your pool further tested for leaks, by sonar testing, and pipe pressure testing.