Turn Off the Water and Locate your water meter
Before you look for leaks, make sure no water is being used inside or outside of your home. About 90 percent of all area residential water meters are located in one of the front corners of your property outside chain link fencing.
The first step is to check your water meter for movement. Look at the sweep hand (normally colored red) on the register to indicate water loss. If the sweep hand is moving, you may have a leak.
** Check Your Toilets **
(This is the most common problem in households and can end up wasting over 100,000 gallons per month, costing customers over $120 water bill per month)
The most common cause of leaks are toilets. Replacing worn rubber toilet flappers usually corrects the problem. To test for a toilet leak, place a drop of food coloring in the toilet tank. If the color shows up in the bowl within 5 minutes without flushing, you have a leak
Check Your Irrigation System
Shut off the anti-siphon valve that serves your sprinkler system. Check the sweep hand at the water meter. If it has stopped moving, then sprinkler system is the problem.
Check Your Water Softener
Most softeners have a bypass lever. Turn the lever to allow water to bypass the softener. Check the flow indicator at the meter. If the flow indicator is no longer moving, you have isolated the leak to your softener. (You also can check for leaking swamp coolers, water-cooled air conditioners, ice machines and reverse osmosis units by turning the bypass lever on each and checking the meter.)
If you are not able to find the leak, you may want to consider contacting a professional plumber to locate and fix the leak(s). If you find a simple leak like your toilet flapper or kitchen faucet, you may want to fix the problem yourself.