This guide helps you understand the signs. It cannot diagnose your property, and more than one cause may be present.

Signs worth investigating

  • A wet area that persists or spreads even when the weather is dry.
  • A patch that changes after a shower, bath or other plumbing is used.
  • Unexpected metered water use after all normal water use has stopped.
  • Repeated loss of boiler pressure, which can also indicate a different heating-system fault.

None of these signs proves there is a hidden leak. Toilets, appliances, seals and visible fittings can also explain unexpected water or damp. Start with what is safely accessible.

What a water meter can tell you

Follow your own water supplier’s instructions. First make sure you have the correct meter and account for all water use, including toilet cisterns, appliances and automatic refilling. Unexpected recorded use may justify further checks.

The Thames Water test linked below closes the internal stop valve to check the supply pipe between that valve and the meter. It does not test the plumbing beyond the closed valve. Follow your supplier’s instructions for the part of the system you want to check. A still meter is not an all-clear: it cannot exclude a leak that is inactive during the test or water escaping from waste pipes. A sealed heating circuit can also lose water without drawing more through the meter until it is refilled.

Read Thames Water’s supply-pipe leak test

Plumber or leak detection specialist?

If you can see water escaping at a fitting, a plumber is usually a sensible first contact. Recurring boiler pressure loss needs a suitably qualified heating engineer.

When the source is hidden, a leak detection specialist can discuss appropriate tests. The investigation may involve more than one method. Non-invasive detection aims to limit disruption, but it does not guarantee that floors or walls will stay untouched. Access may still be needed to confirm or repair a leak. Ask what the proposed visit includes and whether access or follow-up repair is likely to be needed.

Call ADI Leak Detection on 0333 567 2642, the dedicated number for Damp or Leak enquiries, to discuss suitable checks for a suspected hidden leak.

If there is active water damage

Keep away from wet electrical fittings and from under any bulging or sagging ceiling. Do not touch wet switches, sockets or a wet fuse box. If you can safely reach your internal stop tap and know how to use it, turn off the water. Contact an emergency plumber or your landlord’s emergency repairs service.

Do not wait for an online checker if there is a safety concern. If there is immediate danger to life, call 999.

Further reading

The image is illustrative, not a photograph of a diagnosed property. Sources inform this general guide; their inclusion does not imply endorsement.

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