In most situations, yes — a New Zealand homeowner can fit a simple rainwater diverter to redirect roof water into a storage tank without needing a licensed plumber or building consent. However, the rules depend on how you intend to use the water, the size of the installation, and your local council's requirements. Read on before you pick up a hacksaw.
What Is a Rainwater Diverter?
A rainwater diverter (sometimes called a first-flush diverter or tank diverter) is a fitting inserted into your downpipe that redirects water into a storage tank. Most are simple push-fit or clip-on devices that require only basic tools to install. They typically include a first-flush chamber that discards the initial dirty runoff from the roof before cleaner water flows into the tank — an important feature for water quality.
Is This Restricted Work Under NZ Law?
This is the key question. Under the Plumbers, Gasfitters, and Drainlayers Act 2006, plumbing work is restricted to licensed practitioners. However, collecting rainwater into a tank that is used only for outdoor, non-potable purposes (such as garden irrigation, toilet flushing via a separate system (note: connecting to toilet cisterns inside the house involves restricted plumbing work — confirm with the PGDB or your council), or washing the car) is generally considered outside the scope of restricted plumbing work when it involves only a downpipe diverter and a standalone tank.
The situation changes if you want to:
- Connect the tank to your home's internal plumbing (e.g., to supply toilets, laundry, or taps inside the house)
- Use the water for drinking or cooking (potable supply)
- Install a pump connected to household pipework
Any of those scenarios involves restricted plumbing work and must be carried out by a licensed plumber registered with the PGDB. Always confirm the scope with your local council before starting.
Do You Need a Building Consent?
For a simple diverter and a small standalone tank, building consent is often not required under Schedule 1 of the Building Act 2004. However, this depends on the tank size, how it is supported, and your council's interpretation. As a guide:
| Installation type | Consent likely needed? |
|---|---|
| Small diverter + freestanding tank (garden use) | Usually not — confirm with council |
| Large tank (over ~10,000 L) or elevated tank | Possibly yes — check with council |
| Connection to internal household plumbing | Yes, and licensed plumber required |
| Structural support or foundation work | Possibly yes — check with council |
Always check with your local council before starting. Requirements vary between territorial authorities, and MBIE Building Performance provides general guidance on Schedule 1 exemptions.
What the NZ Building Code Says
The NZ Building Code clauses most relevant here are G12 (Water Supplies) and E1 (Surface Water). G12 sets requirements for water quality and supply systems — which is why connecting rainwater to potable supply is tightly regulated. E1 deals with stormwater management; redirecting downpipe flow to a tank can affect stormwater drainage, so make sure overflow from your tank is directed back to the stormwater system or a suitable soakage area, not onto a neighbour's property or a public footpath.
BRANZ has useful technical guidance on rainwater collection systems if you want to dig deeper into best-practice design.
How to Fit a Basic Downpipe Diverter — Step by Step
What you'll need
- Rainwater diverter kit (available at Bunnings or Mitre 10)
- Hacksaw or pipe cutter
- Tape measure and pencil
- Drill and hole saw (if running a hose through a wall or fence)
- Teflon tape or rubber seals (usually supplied)
- A suitable storage tank positioned close to the downpipe
Steps
- Position your tank as close to the downpipe as practical. Ensure it sits on a firm, level base — a concrete pad or compacted gravel is ideal for larger tanks.
- Measure and mark the downpipe at the height specified in your diverter kit instructions (typically 200–400 mm above the tank inlet).
- Cut the downpipe cleanly with a hacksaw. Deburr the cut edges.
- Insert the diverter fitting following the manufacturer's instructions. Most clip or push into place with rubber seals.
- Connect the outlet hose from the diverter to your tank inlet. Keep the run as short and straight as possible.
- Check the overflow outlet on your tank is directed safely away — back to the downpipe continuation or to a soakage area.
- Test with a hose before relying on rain, and check all joints for leaks.
Water Quality Considerations
Even for garden use, roof water can carry bird droppings, debris, and contaminants from roofing materials. Never use unfiltered, untreated rainwater for drinking without proper filtration and disinfection systems installed by a qualified professional. Keep the tank covered to prevent mosquito breeding and algae growth. Clean your gutters regularly — this is the single biggest thing you can do to improve water quality. The Energywise website has practical tips on rainwater use in NZ homes.
When to Call a Professional
Call a PGDB-licensed plumber if you want to:
- Connect your tank to any internal household plumbing
- Set up a potable (drinking) rainwater supply
- Install a pressure pump connected to household pipes
- Carry out any work you are unsure about
For larger or more complex installations — including structural tank supports or significant stormwater rerouting — you may also need a Licensed Building Practitioner. You can find qualified local roofers, plumbers, and builders on tradedirectory.co.nz.
Roofing Association of NZ (RANZ)
Licensed Building Practitioner (LBP)
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