Since some water leaks are very slow or periodic, just glancing at the water meter may not give you any clues, but over time, the meter can give you some information.

Before you go to work:

Turn off the ice maker and the sprinkler system.
 

Run the hot water until the water heater starts to heat - you can hear it when it is on.
 

Read the meter.
 

When you return eight or so hours later, re-read the meter. Compare the readings. If the meter reading has changed and everything was turned off, no one used the water, you have a leak. (Of course there is the possibility that you neighbor is running a hose over to your house to water his yard in your absence. This actually happened to a friend of a friend.)

So, you have a hidden leak, how do you find it?