Checking for Water Leaks Make sure all water is turned off in your house. If it is moving, there is a leak in an underground pipe or in the house. To isolate a leak, turn off the water to your house. There is usually a valve in the basement or crawl space. If it has not stopped, the leak is in the underground pipe, but if it has stopped, the leak is in the house.
Customers find that most in-house leaks result from leaky flush valves or spud washers on toilets.
Fill a one-gallon milk container with water. Recheck the sweep hand. It should have moved by one number.