Free calculator

Hidden water leak test

A higher water bill with no explanation often means a leak you can't see. Turn off every faucet and water-using appliance, read the meter, wait an hour or two without using any water, then read it again.

Two meter readings
Gallons or cubic feet
9-step leak hunt

Gloved hand holding open a water meter box at the curb while a phone waits beside the dial

Use every digit on the meter, including the sweep hand or the small numbers after the decimal; a small leak only moves the last digit. A dripping outdoor faucet or a running toilet during the test will count, which is the point.

Track it down, most likely first

Check the leak indicator on the meterWith every faucet and appliance off, look for a small triangle or star on the meter face. If it's turning, water is moving somewhere.Find the main shutoff and meter
Toilets firstToilets are the most common silent leak. Put a few drops of food coloring in the tank and wait 15 minutes without flushing. Color in the bowl means the flapper leaks.Fix a running toilet
Faucets and showerheadsLook and listen for drips at every faucet, tub spout and showerhead, including the ones in a guest bath.Stop a dripping faucet
Under every sinkDry the cabinet floor and connections, then check with a paper towel after a while.Find a leak under the sink
Water heaterCheck the drain valve at the bottom and the pipe from the relief valve on the side. A slow trickle there can run for months.Water heater leaking
Fridge and ice maker linePull the fridge out and look for moisture around the water line and valve.Refrigerator leaking
Washer hosesCheck both fill hoses and their connections behind the washer.Washing machine leaking
Outdoor faucets and irrigationCheck hose bibs for drips, and look for soggy spots or unusually green patches along sprinkler lines.Outdoor faucet guide
If nothing turns up, shut off the mainTurn off the main shutoff valve at the house and watch the meter. If it still moves, the leak is in the line between the meter and the house, which is a job for a plumber or your water utility.Find your main shutoff

How it works

With nothing using water, any movement on the meter is a leak. The math is simple and shown so you can check it:

Gallons per hour = (second reading − first reading) ÷ hours between them. Cubic-foot meters are converted at 7.48 gallons per cubic foot.

Per day and per year multiply by 24 and 365. Cost is gallons ÷ 1,000 × your water and sewer rate. The bill helper adds your water and sewer charges and converts CCF (100 cubic feet, 748 gallons) to a per-1,000-gallon rate.

The labels are ours: under half a gallon an hour we call a slow leak, up to 3 a real leak, and above that significant. The checklist is ordered by how common each leak is and how easy it is to check, toilets first.

About this tool

Who it's for

For anyone with a water bill that jumped, or a hunch that something is running when it shouldn't be.

Example

You enterMeter reads 48213.4, then 48214.9 two hours later with nothing running

You get0.75 gallons an hour: about 6,600 gallons and $66 a year at $10 per 1,000 gallons.

What's different

Turns two meter readings into a real rate, in gallons or cubic feet.
Walks the likely culprits in order, each linked to its fix.
Ends with the one test that tells you whether the leak is inside or outside the house.

Gotchas and tips

Nobody can use water during the test, including ice makers, irrigation and softeners.
Use every digit on the meter, including the small sweep hand.
A very slow leak may only show on the meter's leak indicator.

Privacy: Runs entirely in your browser. Nothing you type is sent to us, and anything it remembers is saved on this device only.

Built and maintained by the GrabTheHammer team, using the same time, cost and safety notes as our guides. Updated November 2026. Spot a problem? Tell us.