Locate your water meter. It is normally found at the property line in the front yard.
Be sure that no one is using water. Read and record your meter reading.
There is a hand that looks somewhat like a second hand on a watch. Note its position. Observe the position of this hand for 2 to 3 minutes. If it moves there is a leak.
There may also be a small triangle or a star-shaped device on the dial (look at the black triangle near the center of the illustration at the upper right). If it is moving, water is leaking.
You may have a water cut-off valve inside your house, if so, close the valve. If the meter is still moving, your leak is between the meter and the valve location. Look for wet spots in the yard. This type leak is often difficult to locate, so y ou may need to call your local plumber.
If the meter flow indicator hand stops when the cut-off valve is closed, the leak is in the house beyond the cut-off valve. Turn the valve back on and check under the house for leaks.
Check the water level in the commode. It should be at least 1/2 inch below the top of the overflow tube.
Some leaks are very small. A leak that runs 24 hours a day will add up to a large utility bill.
To determine the size of a leak, read your meter before you leave for work or before going to bed--any long period of time when there will be no water usage. (Be sure that icemakers and any other type of automatic watering devices are turned off.)
After several hours, read the meter again. Subtract the difference. This number represents the size of the leak. If your meter registers in cubic feet rather than gallons, multiply by 7.5 to determine the number of gallons leaked.
$$$$ Have any leak repaired quickly. You are responsible for all the water that goes through your meter. Delaying repairs can be costly.