Leaking Underground Drain

Look for more than one clue

Persistent soft ground close to a drainage route, unexplained washout, repeated loss of bedding or visible leakage in a chamber can justify investigation. A damp patch by itself does not prove a drain is leaking.

A camera cannot show every leak

A camera can show the internal condition of the pipe but may not prove whether a hairline defect is leaking under every flow condition. Dye testing or other investigation may sometimes be useful.

Locate the leaking section before choosing the repair

If the leak comes from one short section and the pipe still has a usable shape, a patch or liner may be possible. If the pipe has moved badly or collapsed, the damaged section may have to be dug out.

Some defects leak only when the pipe runs full

A joint may lose water only when the pipe is running full, while a crack above normal flow level may remain dry most of the time. Conversely, a low defect can leak whenever wastewater passes. This is one reason why one still CCTV image may not describe the whole behaviour of the pipe.

Near a building, camera footage is only part of the evidence. Look for washed-out bedding, soft ground or a void close to the same measured point before blaming a small crack for movement or dampness.