Water bill went up for no reason: where to look for a hidden leak

The ten-minute check

Close all taps and appliances. Write down the water meter reading and check it again after ten minutes. If the number has changed or the check dial is moving, water is running somewhere continuously.

• toilet cistern — the most common silent consumer
• taps and the shower mixer diverter
• the water heater's safety valve leaking constantly
• the washing machine connection and tap

If the taps are fine but the reading still moves

Then the leak is likely hidden in the pipework: in a wall, floor or ceiling. Such leaks might not show for a month, but the moisture keeps moving through the structure.

Finding it involves methods such as moisture measurement, acoustic listening and a thermal camera to narrow the area down before opening anything.

Why speed matters

A hidden leak doesn't just mean a water bill. Prolonged moisture damages the ceiling and finishes, and in an apartment building the damage reaches the neighbour quickly.

Where hidden leaks most often start

• connections built into the wall behind the tap and toilet
• the hot water pipe running inside the floor
• old pipework in the ceiling of an apartment building
• water heater connections and the safety valve's drain
• the washing machine's supply hose, which has stayed in the same position for years

How the area is narrowed down before opening

The point of leak detection is to open as small a part of the structure as possible. To do this, moisture readings at different points are compared, pressurised pipework is listened to, and surface temperature differences are checked. This produces the area worth opening.

If the pipework in question is the sewer rather than a pressurised water pipe, a camera inspection gives a clearer picture. Sometimes it turns out the source of moisture isn't the flat's own pipe but the shared stack.

How to document the result

• write down the water meter reading and time before and after the check
• run the same test at night, when no one is using water
• photograph moisture traces on the wall, ceiling or the bottom of a cabinet
• note when consumption increased compared with earlier bills