Striking a buried pipe or cable while digging is one of the most common — and potentially serious — mistakes a homeowner can make. The good news is that with the right preparation, you can significantly reduce the risk before you put a spade or excavator bucket in the ground. Here's what you need to know before digging anywhere on your NZ property.
Why It Matters
Underground services on a typical NZ property can include water supply pipes, stormwater and wastewater drains, gas lines, electrical cables, telecommunications lines, and irrigation pipes. Damaging any of these can result in flooding, sewage spills, gas leaks, electrocution, or expensive repairs — not to mention potential liability for damage to network infrastructure. In some cases, disturbing certain pipes or drains may also trigger building consent requirements, so it pays to check with your local council before you start.
Step 1 — Contact Before You Dig (CBYD)
The single most important step is to use Before U Dig (BUD), New Zealand's free underground service location referral service. Visit beforeudig.co.nz (note: this is a well-established NZ industry service) and submit a request. Utility owners — including electricity, gas, water, and telecom companies — will respond with plans showing where their assets run on or near your property. Allow several business days for responses to come back before you break ground.
Keep in mind that BUD covers network utility assets, not necessarily private pipes on your own property (such as your house drainage or irrigation lines). For those, you'll need to check your own records, council drainage maps, or hire a locator.
Step 2 — Check Council Records and Property Documents
Your local council may hold as-built drainage plans for your property. Contact your council's building or infrastructure team and ask for any available records. Also check your LIM (Land Information Memorandum) report if you have one — it often shows known services. Private drainage and stormwater pipes won't always appear on utility plans, so this step is essential.
Step 3 — Use a Cable and Pipe Locator
Even with plans in hand, services don't always run exactly where the drawings say. Hire or borrow a cable and pipe locator (sometimes called a CAT scanner — Cable Avoidance Tool) to scan the area before digging. These are available for hire from most tool hire shops. A locator can detect live electrical cables and metallic pipes, though it won't reliably find non-metallic pipes (like PVC drains) without a signal transmitter attachment.
For non-metallic pipes, consider hiring a professional with ground-penetrating radar (GPR) equipment, or a drain camera inspection to trace your drainage lines from an access point.
Step 4 — Mark Up the Area Clearly
Once you have service information, use spray paint or marker flags to mark the routes of all known services on the ground. Use the internationally recognised colour coding where possible:
| Colour | Service |
|---|---|
| Red | Electrical |
| Yellow | Gas |
| Blue | Water |
| Orange | Telecommunications |
| Green | Sewer/Drainage |
| Purple | Recycled water / Irrigation |
Mark a buffer zone on either side of each service — typically 500 mm minimum, but check with the relevant utility owner as requirements vary.
Step 5 — Hand Dig Near Known Services
Once you're within the buffer zone of any marked service, stop using mechanical equipment and switch to hand tools. This is called potholing or trial holing — carefully exposing the service by hand so you can confirm its exact location and depth before continuing. Never assume a service is deeper than marked; ground levels change over time and pipes can be shallower than expected.
Key safe digging habits
- Always dig parallel to a service, not across it
- Never use a pick or bar near a known service
- Keep a mobile phone on you in case of emergency
- Know where your property's water and gas shut-offs are located
Step 6 — Know the Depth Rules of Thumb
While depths vary and you should never rely solely on these figures, as a general guide in NZ:
- Water supply pipes are often 450–600 mm deep
- Gas lines are typically 600 mm or more
- Electrical cables vary widely — some are only 300 mm deep in older installations
- Drainage pipes can be very shallow, especially near the house
Always treat any depth information as approximate and verify by hand digging.
When to Call a Professional
Some situations call for a qualified tradesperson or specialist excavator:
- Gas lines: Any work near or on gas pipes must be carried out by a licensed gasfitter. This is restricted work under the Plumbers, Gasfitters and Drainlayers Board (PGDB) regulations. Do not attempt to repair or modify gas pipework yourself.
- Electrical cables: Underground electrical work is restricted electrical work and must be done by a registered electrician licensed under the Electrical Workers Registration Board (EWRB).
- Drainlaying: Connecting to or modifying public drains is restricted work requiring a licensed drainlayer — again regulated by the PGDB.
- Large or complex excavations: If you're hiring a mini-excavator and aren't experienced operating one near services, consider engaging a professional excavation contractor instead.
You can find qualified local excavators, drainlayers, and other tradespeople on tradedirectory.co.nz.
Safety First
If you do strike a pipe or cable while digging:
- Gas leak: Leave the area immediately, don't use any switches or flames, call your gas network operator and 111
- Electrical cable: Do not touch it — call your lines company and 111
- Water or drain pipe: Shut off the supply if safe to do so and call a licensed plumber or drainlayer
For general health and safety guidance on excavation work, refer to WorkSafe NZ.
Licensed Building Practitioner (LBP)
