In most situations, yes — fitting a simple rainwater diverter to an existing downpipe is a task most capable NZ homeowners can tackle themselves. It doesn't typically involve restricted plumbing or drainlaying work, and no building consent is usually required for a basic tank-and-diverter setup. That said, there are some important rules around water supply connections, tank size, and your local council requirements that you need to check before you start.
What Is a Rainwater Diverter?
A rainwater diverter (sometimes called a first-flush diverter or downpipe diverter) is a fitting inserted into your downpipe that redirects roof-collected rainwater into a storage tank or rain barrel. The most common DIY use is filling a garden tank for irrigation. Diverters are widely available at Bunnings and Mitre 10, and typically come as a kit with the diverter body, a flexible hose, and fittings to suit standard 80 mm or 100 mm square or round downpipes.
Is It Restricted Work?
This is the key question. Under NZ law, plumbing and drainlaying work on sanitary plumbing or the drinking water supply must be carried out by a licensed tradesperson registered with the Plumbers, Gasfitters and Drainlayers Board (PGDB).
However, a basic rainwater diverter that:
- Connects to an external downpipe (not internal sanitary plumbing)
- Feeds into a garden/irrigation tank only (not connected to your home's drinking water supply or hot water system)
- Does not involve cutting into or modifying any pressurised water supply pipes
…is generally not considered restricted plumbing work. You're simply redirecting stormwater runoff, which is a straightforward mechanical task.
Important: If you intend to connect your rainwater tank to your home's internal plumbing — for toilet flushing, laundry, or drinking water — that is restricted work and must be done by a licensed plumber. Connecting rainwater to a potable (drinking) water supply also triggers requirements under the NZ Building Code clause G12 (Water Supplies) and may require a building consent. Always confirm with your local council before proceeding.
Do You Need a Building Consent?
For a simple garden tank and diverter, a building consent is generally not required under Schedule 1 of the Building Act 2004, which exempts minor work such as installing a water tank for garden use. However, exemptions can depend on tank size, location, and your specific council's rules. MBIE Building Performance provides guidance on consent exemptions, but always confirm with your local council before starting — this is especially important if your tank is large (over 500 litres is a common threshold some councils flag) or if it's being installed close to a boundary or structure.
What You'll Need
- A rainwater diverter kit (sized to your downpipe — measure first)
- A hacksaw or pipe cutter
- A drill and hole saw (if required by your kit)
- Silicone sealant
- A storage tank with an inlet fitting
- A short length of flexible hose
- Safety glasses and gloves
Step-by-Step: Fitting a Basic Diverter
1. Choose the Right Spot
Pick a section of downpipe that is easy to access and close to where your tank will sit. The tank should be on a firm, level base — a concrete pad or compacted gravel works well.
2. Mark and Cut the Downpipe
Measure the height of your diverter fitting and mark the cut lines on the downpipe. Use a hacksaw or pipe cutter to make clean, square cuts. Remove any burrs with a file.
3. Insert the Diverter
Slide the diverter body into the gap in the downpipe. Most kits use rubber seals or push-fit connectors — follow the manufacturer's instructions carefully. Apply silicone sealant where directed to prevent leaks.
4. Connect the Hose to Your Tank
Run the flexible outlet hose from the diverter to your tank's inlet. Keep the hose as short and direct as possible, with a slight downward slope so water flows freely. Secure connections with hose clamps.
5. Check the Overflow
Make sure your tank has an overflow outlet that directs excess water safely away from your foundation — ideally back to the original stormwater path. This is important for protecting your home's foundation and complying with good drainage practice.
6. Test It
Use a garden hose to simulate rain and check all joints for leaks. Adjust fittings as needed.
Keeping Your Water Safe
Rainwater collected from roofs is not safe to drink without proper filtration and treatment, especially from roofs with lead flashings, treated timber, or certain coatings. Only use diverted rainwater for garden irrigation unless your system has been properly designed and approved for potable use. BRANZ has useful guidance on rainwater quality considerations for NZ homes.
For healthy homes and rental properties, check Tenancy Services for any obligations around water supply and drainage.
When to Call a Professional
You should engage a licensed plumber (find one on tradedirectory.co.nz) if you want to:
- Connect your rainwater tank to internal household plumbing (toilets, laundry, hot water)
- Tie into the mains water supply as a backup or top-up
- Install a pump system with pressurised pipework
- Modify any existing sanitary or stormwater drainage infrastructure
- Deal with complex roof drainage layouts or commercial properties
These situations involve restricted work under the PGDB and may require building consent from your council.
Master Plumbers
