Yes, most homeowners can legally hire a mini excavator and dig their own rainwater tank hole — it's not restricted work in the way that plumbing or electrical jobs are. That said, there are real risks involved: underground services, unstable excavations, and consent requirements can all catch you out. Taking the time to plan properly will save you money, stress, and potentially your life.
Do You Need a Building Consent?
Whether you need a building consent depends on the size and type of tank installation. Under Schedule 1 of the Building Act 2004, some minor work is exempt — but the rules around tanks, retaining walls, and excavations can be nuanced.
- Above-ground tanks are generally exempt from consent if they meet certain size thresholds.
- Below-ground (buried) tanks are more likely to require consent, especially if the excavation affects ground stability or is near a boundary or structure.
- Retaining walls created as part of the excavation may also trigger consent requirements depending on their height — check with your local council for the applicable threshold.
Always check with your local council before you dig. Requirements vary by region and district plan. Don't assume you're exempt — confirm it in writing. You can find general guidance at MBIE Building Performance.
Locate Underground Services First — This Is Critical
Before any excavation, you must identify and mark all underground services on your property. Striking a gas line, water main, or power cable can be fatal and is extremely costly to repair.
- Contact Dial Before You Dig (0800 248 344 or beforeudig.co.nz) to request a service location plan.
- Your local council or network utility operator may also have records of stormwater and wastewater pipes.
- Even with plans, hand-dig carefully around any marked service zones — plans are indicative and services can shift over time.
- Check for septic tanks, soakage fields, and irrigation lines that may not appear on official records.
WorkSafe NZ has clear guidance on excavation safety, including the legal duty to manage risks before breaking ground.
Choosing and Operating a Hired Digger
For most residential rainwater tank holes, a 1.5–3 tonne mini excavator is the right tool. These are widely available from hire companies and are manageable for a capable DIYer.
Key considerations when hiring:
- Access: Can the machine physically get to the dig site? Check gate widths, slopes, and overhead obstacles like power lines.
- Operator training: You don't need a formal licence to operate a mini excavator on private property in NZ, but you do need to be competent. Most hire companies will give you a brief induction — take it seriously.
- Ground conditions: Waterlogged, sandy, or clay-heavy soils can behave unpredictably. If in doubt, get a geotechnical opinion.
- Spoil (excavated soil): Plan where the dirt will go. A typical 5,000-litre tank hole produces a significant volume of spoil that needs to be carted away or spread on site.
Excavation Safety — Don't Skip This
Excavation is one of the most dangerous DIY activities. Soil can collapse without warning, and even a shallow trench can trap and suffocate a person.
| Excavation depth | Risk level | Recommended precaution |
|---|---|---|
| Under 1.0 m | Lower | Still batter sides or shore if soil is loose |
| 1.0 m – 1.5 m | Moderate | Batter sides to a safe angle or use shoring |
| Over 1.5 m | High | Shoring or benching required; consider a professional |
- Never enter an unsupported excavation deeper than 1.5 m.
- Keep spoil piles well back from the edge (at least 1 m) to avoid surcharge collapse.
- Fence or barricade the hole when not actively working — especially if children are present.
- Have a second person on site whenever possible.
Refer to WorkSafe NZ for the excavation safety code of practice.
Plumbing Connections Are Restricted Work
Once the tank is in the ground, connecting it to your roof drainage system or household plumbing is a different matter. In New Zealand, certain plumbing work is restricted and must be carried out by a licensed plumber or drainlayer registered with the Plumbers Gasfitters & Drainlayers Board.
- Connecting a rainwater tank to your drinking water supply (even as a backup) is restricted work.
- Connecting to internal household plumbing for toilet flushing or laundry is also restricted.
- Simple overflow and first-flush diverter connections to a garden-use-only tank may be DIY-able, but check with your council and a licensed plumber to be sure.
For guidance on rainwater use and the NZ Building Code clause G12 (Water Supplies), visit MBIE Building Performance.
Healthy Homes and Rental Properties
If you're installing a rainwater tank on a rental property, be aware of your obligations under the Tenancy Services Healthy Homes standards. Potable water supply requirements still apply, and any changes to water supply must meet the Building Code.
When to Call a Professional
Consider hiring a qualified excavator operator or contractor if:
- The dig site has poor access or difficult ground conditions.
- The excavation is deeper than 1.5 m.
- You're unsure about underground services in the area.
- The site is on a slope or near a retaining wall or building foundation.
- You've never operated an excavator before and feel uncertain.
A professional excavator will work faster, safer, and often more cost-effectively than a first-time operator on a tricky site. You can find qualified local excavation contractors on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
