How to Use Your Water Meter to Check for a Hidden Leak

Why this matters

A water bill that jumps with no change in how you use water usually means water is going somewhere you cannot see: a toilet that runs silently into its bowl, a dripping line under a slab, a pipe in a crawlspace, or the buried line between the meter and the house. Your water meter answers the first question for free in about an hour: is water moving when nothing in the house is using it? A second, shorter test with the main valve closed answers the next one: is the leak inside the house, or between the meter and the house? That tells you who to call, and it saves a plumber's first hour of looking.

What you are reading

Meters differ, but most residential faces carry the same three things. This one is an example; yours prints its own units and values.

 +------------------------------------------+
 |  WATER METER                 GALLONS     |
 |                                          |
 |  REGISTER:   1  4  8  2  3  6 . 4        |
 |              whole gallons    tenths     |
 |              (black digits)   (red)      |
 |                                          |
 |  SWEEP HAND:  one full turn = 1 gallon,  |
 |               marks 0 to 9 in tenths     |
 |                                          |
 |  LEAK INDICATOR:  small red triangle or  |
 |  star; turns with any flow at all, even  |
 |  a few drops a minute                    |
 +------------------------------------------+

The register is the running total, like a car's odometer. It may count gallons or cubic feet; the face says which. One cubic foot is 7.48 gallons, and many bills count in hundreds of cubic feet (748 gallons each) or in thousands of gallons.

The leak indicator is the fastest tell. Because it turns at even a tiny flow, it shows a slow leak in a minute or two that the register would take an hour to show.

A digital meter may show the register on a screen that cycles through several readings, and some show a flow rate or a leak symbol. Many utilities with these meters also offer an online usage portal showing use hour by hour. If yours does, look at the small hours of the night: use that never drops to zero at 3 a.m. is the same signal as a turning leak indicator.

Finding the meter, and opening it safely

The meter is usually in one of three places: a pit near the street or sidewalk under a round or rectangular lid, the basement where the water line comes in, or on an outside wall in mild climates.

A pit lid can be heavy. Lift it with a screwdriver or a meter key through its hole rather than your fingers, and look in with a flashlight before reaching: pits collect water, insects and sometimes animals. Wipe the meter's face clean rather than putting your hand in deep. Leave the valve on the street side of the meter alone; it belongs to the utility and needs their key. See related: Whose Pipe Is It: What the Utility Owns and What You Own.

Test 1: Is water moving when nothing is using it?

1. Stop every use of water, inside and out. Faucets, showers, toilets (wait until each tank finishes refilling), washer, dishwasher, the ice maker (switch it off at the refrigerator), lawn irrigation (set the controller to off), outdoor hoses, a pool's automatic fill, a whole-house humidifier, an evaporative cooler. If you have a water softener, test when it is not regenerating, which many do in the middle of the night. If you have a reverse osmosis filter under the sink, it may keep drawing water to refill its tank for a while; close its supply valve or give it time.

Why: each of these is a legitimate use that looks exactly like a leak on the meter. Miss one and the test reports a leak you do not have.

2. Watch the leak indicator for two minutes. If it is perfectly still, there is no measurable flow right now. If it turns, even slowly, water is moving.

3. Write down the register, every digit, and the time. Include the tenths, or read the sweep hand.

4. Wait an hour without using any water. Nobody flushes, runs a tap or starts an appliance. An overnight wait works too, as long as nothing runs on a timer.

5. Read the register again and subtract. The difference, over the time you waited, is your leak rate.

What breaks if you skip the wait: a still indicator over two minutes misses a toilet that only leaks between refills, every 20 minutes or so. The hour catches it.

Test 2: Inside the house, or before it?

Do this only if Test 1 showed water moving.

1. Close the main water valve where the line enters the house. See related: How to Close Your Main Water Valve and Fixture Stops.

2. Read the register and the time, wait 30 minutes, and read again. Watch the indicator too.

3. Open the main again slowly when you are done, then open one faucet briefly to clear the air from the pipes.

Why this works: closing the main cuts the house off from the meter. If the meter stops, everything that was leaking is on the house side of that valve. If it keeps moving with the main closed, the water is going somewhere between the meter and the valve: usually the buried service line.

The catch: an old main valve may not close completely. If yours is a round-handle valve that turns many times, and the meter keeps creeping after you close it, the valve itself may be letting water by, and the test cannot tell the two apart. That is worth telling the plumber, who can check the valve first.

Reading the result, and who to call

If you see water bubbling up in the yard, a wet patch that never dries, or water in the meter pit, mention it on the call.

Worked example: a bill that went up by half

The house: a meter in a pit by the sidewalk, reading in gallons, with a red tenths digit and a red triangle leak indicator. The last bill was about one and a half times the same month last year, with the same household and no new appliances.

Test 1, 9:00 p.m. Every tap and appliance off, the ice maker switched off, the irrigation controller set to off, both toilet tanks full and quiet. At the pit, the triangle is turning slowly: about one turn every 20 seconds. The register reads 148236.4.

10:00 p.m. Nobody has used any water. The register reads 148239.4.

148239.4 minus 148236.4 is 3.0 gallons in 60 minutes.

Carried forward, 3.0 gallons an hour is 3.0 times 24, or 72 gallons a day, and 72 times 30 is 2,160 gallons over a 30-day billing period. If this utility billed in hundreds of cubic feet, that would be 2,160 divided by 748, about 2.9 units of the bill, every month, for nothing.

Test 2, 10:00 p.m. The main valve, a lever valve in the basement, is closed. The register still reads 148239.4. At 10:30 it still reads 148239.4, and the triangle has not moved. The leak is inside the house.

The toilet check. Toilets are the most common silent inside leak, so before calling anyone, the homeowner opens the main again and puts a few drops of food coloring in each toilet tank, then waits 15 minutes without flushing. The upstairs bowl turns blue; the downstairs one stays clear. The upstairs flapper, the rubber seal at the bottom of the tank, is letting water trickle into the bowl, and the tank keeps refilling to make up for it. A worn flapper is a part many homeowners replace themselves using the instructions on the new one's package; a plumber does it too.

Confirming the fix. After the flapper is replaced, they run Test 1 again: the triangle stands still for two minutes, and the register shows no change after an hour. They file both sets of readings, with dates, in their house records. See related: Your House Records File and What Goes In It.

What would have changed it:

• If the register had kept climbing with the main closed, the leak would have been on the service line between the meter and the house, and the call would have gone to a plumber, with a note that the pit and the yard looked dry. If water had been showing at the meter itself, the utility would have been the call.
• If neither toilet had shown color, the leak would still be inside the house but not at a toilet, which points to a dripping water heater relief line, a crawlspace or under-slab pipe, or a fixture they had not checked. That goes to a plumber with the 3.0 gallons an hour figure, which tells them how big a leak they are looking for.

Make it a habit

Read your meter at the same time on two days a week apart and subtract. It gives you a weekly baseline for your household, and a week that comes in well over it, with nothing to explain it, is the cue to run Test 1. Some households also add water sensors near water heaters and washers. See related: Leak Sensors and Automatic Water Shutoffs.

References

• See related: Whose Pipe Is It: What the Utility Owns and What You Own
• See related: How to Close Your Main Water Valve and Fixture Stops
• See related: Your Home's Shutoffs: Water, Gas and Electric
• See related: Leak Sensors and Automatic Water Shutoffs
• Your water utility's published guidance on reading its meters, which names the units and the leak indicator on the models it installs