Here's how to test for a leak on your water system. Shut off all the fixtures in your home and put red food coloring in all of your toilet tanks. Check the reading on the water meter. Wait at least one hour and recheck the toilets and the reading. If the water in any toilet bowl is red, then the toilet is leaking. If the water has not left the toilet tanks and entered the bowls, but the reading on the water meter has moved even slightly you have an underground leak. A plumber or leak detection company can use a sounding device to locate leaks in underground water pipes.