How to Do a Water Meter Leak Test in Under an Hour

A water meter is the most honest instrument in the house. It doesn't care whether the stain on the ceiling is condensation or a pipe, and it doesn't guess. If water is flowing through it while every tap, toilet and appliance is idle, that water is going somewhere. A meter test won't tell you where a leak is, but done properly it tells you whether there is one, roughly how fast it's running, and which side of your internal stopcock it's on. That last point decides who you call next and, in many places, who pays for the repair.

Set aside 30 to 60 minutes. The longer you can leave the house without using any water, the smaller the leak you'll be able to detect.

What you need

• A torch, ideally a head torch so both hands are free
• A phone for photos and a timer
• A notebook, or the log described further down
• A flat-head screwdriver, for meter chamber lids and toilet isolation valves
• Food colouring in a dark shade such as blue or green
• Gloves, because meter chambers collect spiders, silt and standing water

Before you start

Two things can spoil a meter test before it begins.

The first is anything that uses water automatically. That means a washing machine or dishwasher mid-cycle, a water softener due to regenerate, an irrigation timer, a fridge with a plumbed-in ice maker, and anyone in the house deciding to make tea. Tell everyone what you're doing, and put the softener into bypass if it has a bypass valve.

The second is stored water refilling. If your home has a cold water storage tank in the loft, it refills through a float valve after any use downstairs. Start the test while it's still filling and the meter will move for a perfectly innocent reason. Wait until you can no longer hear the tank filling before taking your first reading. After a bath, that can take a while.

The test, step by step

Step 1: Find the meter

Meters tend to live in a few predictable places:

1. In a small chamber at or near the property boundary, under a metal or plastic lid set into the pavement, drive or front path. Lift it with a screwdriver. The meter face may be under a further flip cover and a layer of insulation.
2. In a box on an outside wall, opened with a simple key or by pressing a catch.
3. Indoors, where the supply pipe enters the house: under the kitchen sink, in a basement, or in a utility room.
4. In flats, in a shared meter cupboard on a landing or in a ground-floor plant room.

If you can't find yours, your water supplier can usually tell you where it is. One caution for flats: if a single meter serves several homes, this test can't separate your usage from your neighbours', and you'll need a different approach.

Step 2: Find the internal stopcock

This is the valve that shuts off water to the whole house. It is commonly under the kitchen sink, near the front door, under the stairs or in an airing cupboard, and in flats it's sometimes hidden behind a bath panel. Check that it turns. Old stopcocks seize, and forcing one can snap the spindle or start a leak at the gland. If yours is stiff, stop, have it looked at, and come back to the test afterwards.

Step 3: Learn to read the meter

Mechanical meters usually show a row of digits. The black digits are whole cubic metres. The red digits or small dials are fractions, typically hundreds, tens and single litres. One cubic metre is 1,000 litres. Many meters also have a small leak indicator: a star, triangle or toothed wheel that spins with even a very small flow, long before the litre digits move.

Digital meters vary. Some show a reading only after you shine a torch on the display, some show a flow rate, and some show a tap or leak symbol. Your supplier's website usually explains what their display means.

Step 4: Watch the leak indicator

With everything off, watch the leak indicator for two full minutes. A steady turn means water is flowing. A single small twitch just after a tap has been closed, followed by stillness, is only pressure settling in the pipe. Write down what you saw.

Step 5: Take two readings

1. Photograph the meter and write down the full reading, including every red digit, with the time.
2. Leave the house's water completely unused for at least 30 minutes. Sixty is better for slow leaks.
3. Take and photograph a second reading.
4. Subtract the first reading from the second.

Any increase means water flowed while nothing was supposed to be using it. To get a sense of scale, turn it into a daily figure. Five litres in 30 minutes is 10 litres an hour, which is 240 litres a day.

Step 6: Close the internal stopcock and repeat

If the meter moved, close the internal stopcock fully and repeat Step 5, this time for 15 to 30 minutes.

• If the meter stops, the water is being lost somewhere inside the house.
• If the meter keeps moving with the stopcock closed, the loss is between the meter and the stopcock. That usually means the underground supply pipe. It can also mean something connected before the stopcock, such as an outside tap or a pipe to a garage teed off the supply before it reaches the house.

Open the stopcock again slowly afterwards. Opening it fully in one go can disturb sediment and send a bang through the pipes.

Step 7: Check the usual indoor suspects

If the loss is inside, work through these before suspecting a hidden pipe.

Toilets. Add a few drops of food colouring to each cistern and don't flush for 15 to 20 minutes. Colour appearing in the pan means the flush valve is letting water past. Look at the back of the pan with a torch as well; a thin ripple of water running down the porcelain is the same fault. Then close each toilet's isolation valve (a quarter turn with a screwdriver on most) and check the leak indicator again.

Cisterns and tanks. A float valve that doesn't shut fully sends water out through the overflow. Look for an overflow pipe dripping from an outside wall, or water trickling into the pan from an internal overflow.

Outside taps. Check for drips, for a hose left connected and turned on at the tap, and, after a hard winter, for a split pipe behind the wall where it wasn't protected from frost.

Softeners and irrigation. A softener stuck in regeneration sends water down its drain hose without stopping. An irrigation system with a cracked buried pipe often shows itself as a strip of unusually green grass in a dry spell.

The boiler filling loop. On a combi or system boiler, a filling loop left slightly open keeps pushing mains water into the heating circuit, and the excess leaves through the pressure relief valve. If the boiler gauge reads high and the discharge pipe outside is dripping, check that both filling loop valves are shut.

Step 8: Retest after each change

After each repair or isolation, repeat the two readings. A meter that goes still after you shut off one toilet has told you exactly where the water was going.

Tip: photograph the meter face at every reading with the time visible on your phone. Photos settle any argument about a misread digit, and they're useful evidence if you later ask your supplier about a leak allowance, where such a thing exists.

Recording your results

A simple log keeps the test honest. For each reading, note:

• the date and time
• the full meter reading
• whether the internal stopcock was open or closed
• what was isolated (toilets, softener, outside tap, irrigation)
• what the leak indicator was doing
• anything unusual you heard, saw or smelled

Keep the log even when the result looks clear. If you repeat the test in a month, the comparison is often more revealing than either test on its own.

Reading the results

What to do next

If the problem turns out to be a toilet, a tap or an overflow, it is usually a straightforward repair. If the meter points to a hidden leak inside the house, go back over the signs of a hidden water leak and see whether any of them line up with a particular room or wall. That gives a leak detection specialist somewhere to start, and keeps the amount of floor or plaster that has to come up to a minimum.

If the loss is on the supply pipe, contact your water supplier before digging anything. Who is responsible for which length of pipe, and whether the supplier helps with repairs or offers an allowance on the bill, varies a great deal between countries and between suppliers. Don't assume the arrangements you've read about elsewhere apply to you.

For a sealed heating leak, a leaking drain, or a leak you still can't place after all of this, the meter has done its job and the next step is locating equipment. The leak detection hub explains the options and what each one can and can't find.