Water mains and service pipes are found on almost every construction site and can be at shallow depth. Striking a pressurised water main causes rapid flooding of excavations, undermining of adjacent ground, and potential collapse of trench walls. Large-diameter mains can discharge thousands of litres per minute. This talk explains how to locate, protect, and safely work near buried water infrastructure.
Key Hazards
Rapid excavation flooding from striking a pressurised water main
Trench wall collapse caused by water undermining the soil around the strike
Contamination of the potable water supply from construction debris entering the pipe
Workers trapped in flooded excavations unable to escape rising water levels
Control Measures
Obtain up-to-date utility records showing water main locations and depths before excavation begins.
Carry out a CAT and Genny scan and dig trial holes by hand to confirm the exact main position.
Hand dig within 500mm of any identified water main or service pipe using non-metallic hand tools.
Support water mains that are exposed during excavation to prevent joint damage or pipe movement.
Brief all operatives and machine drivers on water main locations and the hand-dig exclusion zone.
Have a valve key and isolation plan prepared in case of accidental water main damage.
Report any damage or leakage on a water main immediately to the water company's emergency number.
Keep excavation pumps available to manage flooding if a water main is accidentally struck.
Do not place spoil heaps or heavy plant directly over identified water main routes.
Emergency / Rescue
If a water main is struck, evacuate the excavation immediately as flooding can be rapid. Close the nearest isolation valve if trained and safe to do so. Call the water company emergency number and 999 if workers are at risk.
Remember
Obtain utility records and use CAT and Genny to locate water mains before any excavation
Hand dig within 500mm of any identified water main using non-metallic hand tools only
Support exposed water mains during excavation to prevent joint damage or pipe displacement
Have a valve key and isolation plan ready in case of accidental water main damage
Evacuate the excavation immediately if a main is struck as flooding can be extremely rapid
Applicable Legislation: Water Industry Act 1991 · HSG47 (Avoiding Danger from Underground Services) · CDM Regulations 2015 · Health and Safety at Work etc. Act 1974