Monitor Your Meter
It's time to check inside you rmeter box. It's usually infront of the house near the curb. Lift the cover aside to expose your water meter. Flip open its hinged lid. It is not uncommon to have dirt in the box due to wind and rain. Don't worry, this does not affect the proper operation of your meter. Simply brush it aside to read the meter face.
With all of the faucets (inside and outside) shut tightly, mark the test-needle by laying a straight-pin or toothpick exactly on top of it.
A half hour later, check the dial again. If the test-needle has moved and no one has used any water you probably have a leak and should do some more investigating.
To determine if the leak is inside or outside the house, locate the main shut-off valve (usually at the front of the house underneath an outside faucet). If the dial moves while the main house valve is turned off, you probably have an underground houseline leak. Inspect along a straight line between the meter and the house valve for surface water or a wet or super-greenspot.
Note: Leaks that may occur intermittently (like a running toilet, irrigation system leak or faulty swimming pool fill valve) will not always continuously register at the meter. These are all early steps you can take to locate the problem your self before calling a plumber or leak detection specialist.
Read Your Meter - Often!
One way to find out the "why" of high water consumption is to determine the "what” and "when” consumption is occuring. Read your meter every day or every week and keep a log of the readings. Is your consumption consistent or is it higher on some days? If your sprinkler system has a timer, read the meter the day before and the day after an irrigation cycle. How much water is going into the garden? How does that compare to the days without irrigation?
You may routinely put new washers in the faucets and fix any leaks you can see inside the house and around the yard but do you have any invisible leaks?