To check for leaks in your home, you first need to determine whether you're wasting water. Then identify the source of the leak.

• Take a look at your water usage during a colder month, such as January or February. If a family of four exceeds 12,000 gallons per month, there are serious leaks.
• Check your water meter before and after a two-hour period when no water is being used. If the meter changes at all, you probably have a leak.
• Identify toilet leaks by placing a drop of food coloring in the toilet tank. If any color shows up in the bowl after 10 minutes, you have a leak. (Be sure to flush immediately after the experiment to avoid staining the tank.)
• Examine faucet gaskets and pipe fittings for any water on the outside of the pipe to check for surface leaks.

Source:  U.S. Environmental Protection Agency website