In many cases, yes — you can install certain types of water filters onto your kitchen cold tap yourself, without needing a licensed plumber. However, the answer depends on the type of filter system you choose and how it connects to your plumbing. Some installations cross into restricted plumbing work under NZ law, which must be carried out by a licensed tradesperson.
Types of Water Filters Available in NZ
Understanding the different filter types will help you decide what's within DIY reach.
Bench-top or Countertop Filters
These sit on your benchtop and connect to your existing cold tap via a diverter valve that screws onto the tap's aerator thread. No cutting of pipes is required. This is generally considered a straightforward DIY task for most homeowners — if your tap has a standard aerator thread, you simply unscrew the aerator and attach the diverter fitting supplied with the unit.
Faucet-Mounted Filters
Similar to bench-top units, these clip or screw directly onto the end of your tap spout. Again, no pipe work is involved, making these a practical DIY option.
Under-Sink Filters (Inline)
These are installed beneath the kitchen sink and connect inline with the cold water supply pipe. This typically involves cutting into the existing pipe and fitting a T-piece or saddle valve. In NZ, any work that involves cutting, joining, or modifying water supply pipework is classified as restricted sanitary plumbing work under the Plumbers, Gasfitters and Drainlayers Act 2006. This work must be carried out by — or supervised by — a licensed plumber.
Reverse Osmosis (RO) Systems
RO systems are more complex under-sink units that also require a dedicated drain connection and sometimes a separate filter tap. Because they involve both supply pipework and a drain connection, they almost always require a licensed plumber.
Whole-House or Inline Mains Filters
These are installed on the main cold water supply line, usually near the toby valve or where the mains enters the house. This is definitively restricted plumbing work and must be done by a licensed professional.
What Is Restricted Plumbing Work in NZ?
Under NZ law, restricted sanitary plumbing work includes any work on water supply pipes, fittings, or drainage inside a building. Only a person registered and licensed by the Plumbers, Gasfitters and Drainlayers Board (PGDB) can legally carry out this work. Doing restricted work yourself — or hiring an unlicensed person — can result in fines, insurance issues, and problems when you sell your home.
The key rule of thumb: if it involves cutting or modifying a pipe or drain, it's restricted work.
What a Homeowner CAN Do
- Attach a bench-top or faucet-mounted filter to an existing tap aerator thread
- Replace filter cartridges inside an existing filter housing
- Connect a filter unit using the flexible hose and diverter valve supplied by the manufacturer (no pipe cutting involved)
- Install a filter on a garden hose fitting for outdoor use
Always follow the manufacturer's installation instructions carefully, and check that any fittings are compatible with your tap before purchasing.
What Requires a Licensed Plumber
- Any work that involves cutting, joining, or modifying water supply pipes
- Installing a saddle clamp or T-piece into existing pipework
- Connecting a filter unit to a drain or waste pipe
- Installing a dedicated filter tap (requires a new hole in the benchtop and a new supply connection)
- Installing whole-house or mains-pressure inline filters
If you're unsure whether your planned installation crosses into restricted work, contact the PGDB or a licensed plumber for advice before you start.
Does It Need a Building Consent?
Most water filter installations are minor enough to fall under Schedule 1 exemptions of the Building Act 2004 and won't require a building consent. However, this can depend on your specific situation and local council requirements. Always check with your local council if you're unsure — don't assume an exemption applies.
For more on the NZ Building Code and consent requirements, visit MBIE Building Performance.
Choosing the Right Filter for NZ Water
NZ tap water quality varies by region. Some areas have naturally soft water; others may have higher sediment, chlorine, or other minerals. Check with your local council or water supplier about what's in your water before choosing a filter type — this will help you select the right filtration media (carbon block, sediment, UV, RO, etc.).
You'll find a range of filter systems at Bunnings, Mitre 10, and PlaceMakers, as well as specialist water filter suppliers.
Safety Note
Always turn off the water supply before attempting any connection near your plumbing, even for simple diverter-valve installations. After installation, check all connections carefully for leaks before leaving the system unattended. If you notice any drips or moisture under the sink, turn off the supply and investigate immediately — even a slow leak can cause significant water damage over time.
When to Call a Professional
If your chosen filter system requires any pipe modifications, a new tap, or a drain connection, call a licensed plumber. It's also worth getting a plumber involved if you're not confident working around your under-sink plumbing, or if your existing pipework is old or in poor condition. A qualified plumber can also advise on the best filter type for your home's water supply.
You can find licensed local plumbers on tradedirectory.co.nz — look for someone with current PGDB registration.
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