Check your water meter
Turn off all the water in your home. Shut off all faucets, and make sure the dishwasher, washing machine, and hot water heater are not running. If the meter dial is still spinning, you likely have a leak. The leak could be anywhere after the meter, or even underground. Remember that all piping after the meter is a homeowner’s responsibility.
Check your toilets
Toilets can account for up to 30 percent of your water use, so you should check to ensure they’re running properly. To test for leaks, add a few drops of food coloring to your toilet tank and wait 10 minutes. If the color shows up in your bowl, then you have a leak allowing water to flow from the tank to your drain without ever flushing the bowl
Isolate the leak
Do you have a shut off going into your house? If so, shut it off and re-check the meter. This will tell you if the leak is underground between the house and meter.