Detect leaks in a pool by using the bucket test and by measuring the water level with the pool's pump on and off. Pools normally lose a certain amount of water due to evaporation and splash off, so a drop in water level may not mean there is a leak.
Fill the swimming pool up to full capacity. Use a piece of duct tape to mark the water level. Fill a bucket of water, and place it right next to pool. Mark the water level inside the bucket. Leave the bucket next to the pool for a few days. If the water level in the pool has dropped substantially more than the level in the bucket, then this may mean that the pool has a leak.
In order to discern if the leak is in the plumbing or the shell of the pool, fill the pool up to capacity once again. Mark the water level and turn the pool's pump on. Leave the pump running for 12 to 24 hours, and check the pool's water level again. If the water level decreases, then there is most likely a leak on the pressure side of the pool plumbing.
Fill the pool up again, and turn the pump off. Let the water in the pool sit for the same amount of time as when the pump was running. If the water level drops more than while the pump was running, then the leak is on the vacuum side of the plumbing.