First, check for a possible leak inside your home. The most common causes of leaks are dripping faucets or toilets. You can get toilet tank leak detector tablets or place a few drops of food coloring in the toilet tank. If any color appears in the bowl, the toilet is leaking. If your toilet is not leaking, the next most likely reason may be an outside leak or lack of efficient water use, possibly outside irrigation. The best way to determine if your irrigation system is leaking is by looking at your lawn. If you notice wet spots or pooling of water around your spray heads, this is a good indication that your irrigation system has a leak. If you have a layout of your irrigation system, start tracking the lines to determine the exact location.