Yes, in most cases you can install a basic rainwater tank to water your garden — and it's a great way to reduce your water bill and keep the garden green during dry spells. However, there are a few important rules around consents, connections, and water safety that you need to understand before you start.
Do You Need a Building Consent?
For a freestanding rainwater tank used solely for garden irrigation (not connected to your home's internal plumbing), a building consent is generally not required under Schedule 1 of the Building Act 2004. This exemption typically applies to tanks that are not structurally part of the building and don't supply water for drinking, cooking, or sanitary use.
However, consent requirements can vary depending on your local council, the size of the tank, and how it's installed. Always confirm with your local council before you begin — what's exempt in one region may require consent in another. You can find general guidance on exemptions at MBIE Building Performance.
What You Can Do Yourself
As a homeowner, you can generally handle the following tasks yourself:
- Choosing and positioning the tank — place it on a firm, level base (concrete pad or compacted gravel) close to a downpipe
- Preparing the base — a solid, level foundation is essential, especially for large tanks that become very heavy when full (water weighs 1 kg per litre)
- Connecting a first-flush diverter to the downpipe to keep debris and contaminants out of the tank
- Installing a basic tap or hose fitting at the tank outlet for gravity-fed garden watering
- Fitting a mosquito-proof screen over the inlet and overflow — this is important for public health
- Overflow pipe routing — directing overflow away from foundations and onto a garden or soakage area
What Is Restricted (Licensed Trades Required)
This is where many DIYers get caught out. If you want to connect your rainwater tank to any part of your home's plumbing system — including an outdoor tap that's plumbed into the house, a pump connected to internal fixtures, or any supply used for drinking or sanitation — that work is restricted plumbing under the Plumbers, Gasfitters and Drainlayers Act 2006.
Only a licensed tradesperson registered with the Plumbers Gasfitters & Drainlayers Board can legally carry out that work. Connecting rainwater to your mains supply without proper backflow prevention is also a serious health and safety risk — it can contaminate your drinking water supply.
Similarly, if you're installing an electric pump with any fixed wiring, that electrical work must be done by a registered electrician licensed through the Electrical Workers Registration Board. Plugging a pump into a standard outdoor GPO (general power outlet) is generally fine for homeowners, but any new wiring or outlet installation is restricted electrical work.
Choosing the Right Tank
Rainwater tanks come in a wide range of sizes and materials. Common options in NZ include:
| Type | Typical Size Range | Notes |
|---|---|---|
| Poly (polyethylene) | 200 L – 30,000 L | Lightweight, UV-stabilised, popular choice |
| Slimline poly | 400 L – 5,000 L | Good for narrow side yards |
| Corrugated steel (Aquaplate) | 5,000 L – 100,000+ L | Durable, suits rural properties |
| Bladder/flexible | 200 L – 10,000 L | Can fit under decks |
For a basic garden setup, a 1,000–5,000 litre poly tank is a practical starting point for most suburban sections. You'll find a range of options at Bunnings or Mitre 10, and specialist tank suppliers around NZ.
Key Installation Tips
- Solid base is non-negotiable — an unstable base can cause a full tank to tip or crack
- Raise the tank slightly if you want better gravity-fed water pressure to your hose
- Install a first-flush diverter — the first flow of water off a roof carries the most bird droppings, dust, and debris
- Fit a leaf filter at the downpipe entry point
- Label the tank clearly as non-potable (not for drinking) if there's any chance someone might use it for that purpose
- Check your roof material — roofs treated with certain coatings or made from materials like old asbestos-cement should not be used to collect water, even for garden use. Check with BRANZ if you're unsure about your roof
- Overflow management — make sure overflow doesn't pond near your foundations, which could breach NZ Building Code clause E1 (Surface Water)
NZ Climate Considerations
New Zealand's rainfall is highly variable — Auckland gets rain fairly regularly year-round, while Canterbury and Central Otago can have long dry summers. A tank that fills quickly in Wellington may take weeks to refill in Hawke's Bay after a dry spell. Size your tank to match your local rainfall patterns and garden water needs. Energywise has useful information on water conservation and efficiency.
When to Call a Professional
Call a licensed plumber if you want to:
- Connect the tank to any household plumbing or fixtures
- Install a pump that supplies water to the house
- Set up automatic switching between mains and tank supply
Call a licensed electrician if you need fixed wiring for a pump or any new power outlet.
For larger or more complex installations — including tanks over 25,000 litres, tanks integrated into new builds, or rural potable systems — it's worth consulting a qualified landscaper or civil contractor. You can find experienced local professionals on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
