How to Read a Water Meter to Check for a Leak

Which numbers to read, and what they mean

Most household meters have a row of rolling digits, like an old car mileometer. The black digits, usually on a white background, count cubic metres. One cubic metre is 1,000 litres, roughly twelve or thirteen typical baths. Water bills are charged per cubic metre, so these whole numbers are all you give the water company when it asks for a reading. Ignore leading zeros.

After the black digits come red ones, either as more rolling digits or as small clock-style dials with a needle. They split the cubic metre into smaller parts. On most meters the first red figure counts hundreds of litres, the next tens of litres and the last single litres. Where there are dials, each one is marked 0 to 9 with a multiplier printed beside it, such as x0.1, x0.01 and x0.001. When a needle sits between two numbers, read the lower one.

So a meter showing 00482 in black followed by 3, 7 and 5 in red reads 482.375 cubic metres: 482 whole cubic metres and 375 litres. You would submit 482. For a leak test you would note all of it.

Many meters also have a tiny star, cog or triangle-shaped wheel near the digits. That is the flow indicator. It spins whenever any water at all is passing through the meter, even a trickle too small to move the last red digit quickly, which makes it the single most useful thing on the meter for spotting a leak.

The 30-minute leak test, step by step

Water companies suggest a version of this check before they send anyone out. It takes half an hour and needs nothing but a pen.

• Turn off every tap, and make sure the washing machine, dishwasher, water softener and any outside hose are not running
• Wait until every toilet cistern has finished refilling
• Close your inside stopcock, usually under the kitchen sink, so that no water can enter the house pipework
• Write down the full reading, black and red, and note whether the flow indicator is still
• Wait 30 minutes without using any water, then read the meter again

If the stopcock will not turn by hand, stop. Forcing an old stopcock can snap the spindle and leave you with water you cannot turn off.

What the result is telling you

If the two readings match and the indicator never moved, there is no leak between the meter and your stopcock. If the numbers went up with the stopcock closed, water is escaping somewhere between the meter and the stopcock: usually the underground supply pipe, or an outside tap or garden pipe that branches off before the stopcock. That pipe is yours to repair, and it is usually underground, so you will not see the water. Our page on a water meter running with no taps on covers the next checks.

Now repeat the test with the stopcock open and everything inside still turned off. If the meter only moves when the stopcock is open, the leak is inside the house: a cistern passing water into the pan, a dripping overflow, a weeping joint under a floor, or a combi boiler’s filling loop left slightly open.

The size of the movement matters. A red litres digit creeping by one or two over half an hour is a slow drip, most often a toilet. Ten litres over 30 minutes is 480 litres a day, which is a real leak that you will see on your bill. If the hundreds-of-litres digit has moved, something is running freely and it is worth finding today.

To check toilets on their own, flush, wait half an hour, dry the back of the pan and lay a dry sheet of toilet paper on it. Leave it for at least three hours or overnight. If it is wet or torn, the cistern is letting water past.

Smart and digital meters

Thames Water is fitting smart meters across London that send readings automatically, so you do not need to submit them. Some have a small digital display instead of rolling digits. The principle is identical: whole cubic metres first, then the decimal part in litres, and you can run the same stopcock test by watching the display.

If the display is blank or hard to read, your online account may show hourly or daily use instead. A line that never drops to zero overnight, when nobody is using water, is the smart-meter version of a spinning flow indicator.

Finding and opening the meter safely

Outside meters sit under a small metal or plastic cover in the footpath, driveway or front garden, normally beside the outside stop tap. Inside meters are usually under the kitchen sink next to the stopcock, or in a basement or garage. In flats, look in the communal meter cupboard or the riser. The water meter location guide shows how to match your meter to your bill using the serial number.

Lids in the pavement can be stiff. Use a flat screwdriver or a key in the slot rather than your fingers, keep your face back, and wear gloves, since meter pits collect grit, water and spiders. If the pit is full of water, bail it out first. Water that keeps flowing back in during dry weather is a clue in itself: see a water leak at the meter.

When the meter confirms a leak

An internal leak you can see, such as a dripping joint or a running cistern, is often a quick fix. A leak you cannot find, or one on the supply pipe outside, needs tracing. Thames Water asks you to arrange the repair within four weeks of finding a leak on your supply pipe or of it confirming one, and on a meter you pay for the lost water until it is done. If the repair is made within those four weeks, Thames Water may credit the lost water through its leak allowance, which you claim within three months of the repair.

If the stopcock will not close or will not open fully, the test cannot give you a clean answer, and a stopcock repair comes first. For a leak that is running now, book an emergency leak repair. You pay the £60 call-out and the repair price is agreed with you on site before any work starts.