Working Near Water Mains

Water mains carry pressurised drinking water through a buried pipe network beneath roads, footpaths, and open ground.
Striking a pressurised water main during excavation causes uncontrolled flooding that can rapidly fill trenches and excavations.
Water mains are typically made of cast iron, ductile iron, HDPE, or asbestos cement depending on their age and location.
Some older water mains contain asbestos cement — breaking or cutting them releases asbestos fibres requiring specialist procedures.
The water company must be consulted for main locations, and service plans obtained before any excavation work begins.
CAT and Genny scanning detects metallic water mains, but plastic PE mains produce no signal and may be missed.
Within 500mm of a known water main, only careful hand digging is permitted to avoid damage from machine buckets.
A burst water main can undermine adjacent ground, causing trench walls and road surfaces to collapse without warning.
Support exposed water mains immediately to prevent damage from movement, vibration, or the weight of backfill material.
Water main damage must be reported to the water company immediately — they control the supply network and repair procedure.

Trench flooding	A burst water main fills an excavation rapidly, trapping and drowning workers who cannot escape the rising water.
Ground collapse	Pressurised water escaping from a damaged main erodes surrounding ground, undermining trench walls and road surfaces.
Asbestos cement	Older mains may be asbestos cement — breaking them releases deadly fibres requiring specialist handling and disposal.

Do

Don't

Obtain water main locations from the water company before excavating.
Scan with CAT and Genny, but remember PE mains will not produce a signal.
Hand dig carefully within 500mm of any known or suspected water main.
Identify the pipe material — asbestos cement mains need specialist handling.
Support exposed water mains to prevent damage from movement or backfill loading.
Report any damage to a water main to the water company immediately.
Monitor for signs of water seepage during excavation near known main routes.
Keep trench pumps available when excavating near water mains in case of a burst.
Brief all excavation workers on water main locations and burst procedures daily.
Backfill around exposed mains with the correct surround material as specified.

DON'T excavate near water mains without obtaining service plans from the water company.
DON'T rely solely on CAT scanning — plastic mains are invisible to the instrument.
DON'T machine dig within 500mm of any water main — hand dig with care only.
DON'T cut or break asbestos cement pipes without specialist asbestos procedures.
DON'T leave exposed water mains unsupported in the trench — they can fracture.
DON'T attempt to repair a burst water main yourself — call the water company.
DON'T ignore unexpected water in the trench — it may indicate a damaged main nearby.
DON'T work in deep trenches near water mains without escape ladders readily available.
DON'T assume you know the exact position of a main — records are often inaccurate.
DON'T backfill around water mains with incorrect material — it causes pipe damage.

See also: CAT & Genny Safe Use | Working Near Gas Mains

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