Ensure every single water-using appliance and fixture in and around your home is turned off. This includes all faucets, showers, toilets (ensure they are not running), dishwashers, washing machines, ice makers, and any outdoor irrigation systems or hoses. This step is critical to prevent false positives during the test and to establish a baseline of zero water consumption.

Find your water meter, which is typically located in a concrete or plastic box in the ground near the street or curb. You may need a tool like a large screwdriver or a specialized meter key to pry open the heavy lid. Carefully lift the lid, wearing work gloves for protection. You may need to clear away dirt, leaves, or water from the box to see the meter. Flip open the protective cap on the meter face to reveal the dial.

First, look for the leak indicator on the analog meter. This is usually a small, triangular or star-shaped dial that spins even with very low water flow. If it is moving when you are certain all water is off, you have confirmed a leak. Next, accurately record all the numbers on the meter's odometer-style display. To ensure perfect accuracy, take a clear photo of the meter dial with your smartphone. This will serve as an exact reference point for comparison later.

With all water usage confirmed to be off and the initial meter reading recorded, you must now wait for a significant period without using any water. A duration of 1 to 2 hours is generally sufficient to allow even a slow leak to register a noticeable change on the meter. It is imperative that no one in the household uses a toilet, faucet, or any other water appliance during this time.

After the waiting period has elapsed, return to the water meter and take a second, careful reading. Compare this new reading to the initial one you recorded (or the photo you took). If the numbers on the odometer have increased, or if the large sweep hand has moved from its original position, it confirms you have a leak somewhere in your plumbing system. The next step will be to determine if it's inside or outside.

To determine if the leak is inside the house or in the underground service line, you must now shut off the water supply to the entire house. Locate your home's main water shut-off valve. Based on our assumption, this is in the basement or crawl space where the main water pipe enters the house. It will have either a wheel-like handle (gate valve) or a lever handle (ball valve). Turn the handle clockwise (for a wheel) or perpendicular to the pipe (for a lever) until it is fully closed. This isolates the entire house plumbing system from the incoming service line.

Return to the water meter for one final check. With the house's main valve shut off, carefully observe the small leak indicator again. If the indicator is still spinning, the leak is located in the underground pipe between the meter and your house's shut-off valve. If the indicator has stopped moving, the leak is located somewhere inside your house's plumbing system (e.g., a running toilet, a dripping faucet, or a leaking pipe in the walls). At this point, you have successfully determined the general location of the leak. An underground leak requires professional repair.