Yes, you can generally use a digger (excavator) to help install a rural water tank on your property — and for larger tanks, it's pretty much essential. However, whether the overall project is fully DIY-friendly depends on the tank size, how it connects to your home's plumbing, and your local council's rules. Here's what you need to know before you fire up the machine.
What the Digger Is Actually Used For
An excavator is useful at several stages of a rural water tank installation:
- Excavating the tank pad or pit — especially for in-ground or partially buried tanks
- Levelling and compacting a stable base — critical for large polyethylene or concrete tanks
- Lifting and positioning the tank — some excavators with appropriate attachments can manoeuvre large tanks into place
- Trenching for supply pipes — digging the trench from the tank to your home or outbuildings
- Backfilling — once pipework is laid and inspected
Using the right machine for the job matters. A compact 1.5–3 tonne excavator is often sufficient for residential tank pads and trenching, while larger concrete tanks may need a bigger machine. If you're hiring, make sure the excavator has enough reach and lift capacity for your tank size.
Do You Need a Building Consent?
This is where things get more complex. Under the NZ Building Code, installing a water storage tank may or may not require a building consent, depending on the specifics.
Schedule 1 of the Building Act lists certain exempt building work — some minor tank installations may fall under this exemption, but the rules have conditions and are not always straightforward. Key factors include:
- The size and type of tank (above-ground vs. in-ground)
- Whether it connects to your home's potable water supply
- Whether any structural work is involved (e.g., a concrete pad or retaining)
Always check with your local council before starting work. What's exempt in one district may require consent in another, and getting it wrong can cause headaches when you sell the property or make an insurance claim.
Plumbing Connections — What You Can and Can't Do
This is the most important legal boundary for DIYers. In New Zealand, connecting a water tank to your home's internal plumbing is restricted building work under the plumbing regulations.
Under the Plumbers, Gasfitters and Drainlayers Board (PGDB) rules:
- You may install the tank itself, prepare the site, and lay supply pipes in the ground (in many cases)
- You must use a licensed plumber to connect the tank to your home's potable water system, install backflow prevention, and carry out any work on sanitary plumbing
- Backflow prevention is particularly important — without it, tank water can contaminate your mains supply or vice versa, which is both a health risk and a code violation
If your property is on a rural rainwater-only supply (no mains connection), the rules may be slightly different, but a licensed tradesperson should still commission the final connections and sign off the work.
Choosing and Preparing the Right Base
A stable, level base is critical — a poorly supported tank can crack, tip, or fail, especially once it's full of water (water is heavy: 1,000 litres = 1 tonne).
| Tank Type | Typical Base Requirement |
|---|---|
| Polyethylene (poly) above-ground | Compacted sand or pea gravel, 100–150 mm deep |
| Poly in-ground | Engineered excavation, compacted base, possible concrete ring |
| Concrete tank | Reinforced concrete pad — usually requires engineering sign-off |
| Corrugated steel (Aquaplate) | Compacted gravel or concrete ring beam |
Always follow the tank manufacturer's installation instructions. Brands like Polymaster, Bushmans, and Contain Water Systems publish specific base requirements — check their websites or ask your supplier.
Trenching for Supply Pipes
When trenching from the tank to your home, keep these points in mind:
- Minimum cover depth for water supply pipes is typically 450 mm in NZ (check NZS 4404 and your council's requirements)
- Use UV-resistant, food-grade poly pipe rated for potable water
- Lay pipes with a slight fall toward the tank where possible to allow drainage
- Mark the trench route before digging to avoid existing services — always call Before U Dig (0800 248 344) to locate underground cables and pipes
- Backfill carefully around pipes with fine material before using the bucket to avoid crushing them
Water Quality and Health Considerations
Rural tank water is not automatically safe to drink. BRANZ and public health guidelines recommend first-flush diverters, mesh screens, and UV or filtration treatment for potable rainwater supplies. Your local council's environmental health team can advise on water quality standards in your area.
When to Call a Professional
While the excavation and site prep are well within DIY territory (with the right machine and care), you should engage a qualified tradesperson for:
- All plumbing connections to your home's water supply — this is legally restricted work requiring a licensed plumber (PGDB)
- Large or in-ground concrete tanks that may need engineering input
- Any electrical work for pump systems or UV treatment — restricted work under the EWRB
- Consent applications if your council requires them
You can find experienced local excavators, plumbers, and rural water specialists on tradedirectory.co.nz to help with the parts of the job that need a professional touch.
Licensed Building Practitioner (LBP)
