One of the easiest water leak tests is to place dye in your toilet tank and see if the dye gets into the toilet bowl without having to flush. If so, water is getting by the flapper valve and will need to be serviced. Another uncomplicated test is to read your water meter before going to bed. Then read it again in the morning before using any water. If the readings are the same, there is no leak.
A variation of this test includes:
Locate your water meter. Usually it is in the basement by a wall nearest the street.
Locate the shut-off valve for your home.
For the duration of this test, do not use any water associated with this water service. This includes flushing toilets, using refrigerator water and ice dispensers, humidifiers, irrigation systems, etc. Turn off all water faucets and any appliances that use water.
Check the position of the "1 cubic foot" dial on your water meter and record your reading.
After a period of at least 30 minutes, record another meter reading.
If no leaks are present, the readings should be identical, since no water is being used. Any advancement of the dial would indicate that water is being used somewhere and a leak may be present.
If the needle on the "1 cubic foot" dial is moving, use the shut-off valve to turn off the water to the home.
If the needle stops moving after shutting off the water supply, this would indicate that the leak is inside the house. Check faucets and toilets for slow leaks.
If the needle continues to move after shutting off the water supply to the house, the leak is between the meter and the shut-off valve.
Remember to turn the valve back on when you are done.