Backyard pools can be water wasters, so it's imperative to be aware if your pool is leaking. One way to check is to use a grease pencil to mark your pool's current water level. Wait one day and look at the mark: If the water level is half an inch or lower than the original mark, you likely have a leak. It's important to have a professional inspect the pool and determine where the leak is coming from and repair it. Be sure to cover your pool every night: It reduces the amount of evaporation of water into the atmosphere.