How do I check my house for a hidden water leak?

A hidden leak wastes water, damages the building and can run for months without any visible sign. The meter test is the only reliable way to know whether one exists, and it costs nothing.

What you'll need

• Access to the water meter
• A torch
• A notebook or your phone camera

Step by step

1. Find the meter.Usually in a small chamber in the pavement or the front garden, sometimes inside near the stopcock. Take a torch and something to lift the cover.
2. Turn off every water-using appliance.Dishwasher, washing machine, ice maker, irrigation timer, water softener regeneration. Anything that draws water on its own schedule will invalidate the test.
3. Read the meter precisely.Photograph the whole dial including the small red or black test dial, which registers very small flows. That dial is what detects a slow leak.
4. Leave it an hour with no water used.No toilets flushed, no taps run. An hour is enough for a meaningful leak; overnight is better for a very slow one.
5. Read it again.Any movement at all means water is passing the meter. If the small dial is turning continuously, that is a definite leak.
6. Split the problem at the stopcock.Close the internal stopcock, note the meter, and wait again. If it still moves, the leak is between the meter and the house — the supply pipe, which is usually the homeowner's responsibility.
7. Work through the house if it is internal.Close each isolating valve in turn — toilets first, then appliances, then each bathroom — repeating the meter test after each. The one that stops the movement contains the leak.
8. Check the toilets specifically.A leaking flush valve is the most common hidden leak of all and is completely silent. Put a little food colouring in the cistern and see whether it appears in the pan without flushing.
9. Check the overflow and the heating.Look for water discharging from any overflow pipe outside, and check whether the heating system is losing pressure — those are leaks that never reach the meter test.
10. Look for the physical signs.A warm patch on a floor, a damp skirting, a musty smell, unusually green grass over the supply pipe route, or a boiler that keeps needing topping up.
11. Call the water company if it is on the supply pipe.Most companies offer free leak detection and some contribute to repairs on the supply pipe. It is worth asking before commissioning anyone.

Tips

• The small test dial on the meter is the one that matters. It registers flows too small to move the main digits.
• Do the overnight version if the hourly test is ambiguous. Eight hours of no use is a far more sensitive test.
• Ask your water company before paying for leak detection — many provide it free and some help with repair costs.

Common mistakes

• Testing without turning off the appliances — An ice maker, a softener regenerating, or an irrigation timer will draw water during the test and produce a false positive. Anything on a timer has to be off.
• Assuming no visible damp means no leak — A leak on a buried supply pipe or under a solid floor can run for years without appearing indoors. The meter is the only reliable detector.

If it doesn't work

Questions people ask