Digging a soakhole for a greywater system in NZ is not a straightforward DIY job — while the physical digging may seem simple enough, the regulatory side is where most homeowners get caught out. You'll likely need building consent, must comply with the NZ Building Code, and the plumbing connections are restricted work that must be done by a licensed tradesperson. Read on to understand exactly what's involved before you pick up a spade.
What Is a Greywater Soakhole?
A greywater soakhole (sometimes called a soakpit or absorption pit) is an underground structure designed to disperse greywater — wastewater from sinks, showers, baths, and laundry — into the surrounding soil. It is distinct from a blackwater system, which handles toilet waste and requires a septic tank or connection to a reticulated sewer.
Greywater soakholes are most commonly used on rural or lifestyle properties not connected to a public sewer, though some urban properties also use them for specific purposes such as laundry or rainwater overflow.
Do You Need Building Consent?
In most cases, yes — building consent is required for a new greywater disposal system, including a soakhole. Greywater disposal is covered under NZ Building Code clauses G13 (Foul Water) and sometimes E1 (Surface Water), depending on your setup.
Some very minor drainage work may fall under Schedule 1 exemptions to the Building Act 2004, but greywater systems are generally not exempt because they affect public health and the environment. Always check with your local council before starting any work — rules vary significantly between territorial authorities, and some councils have specific greywater bylaws or require resource consent as well as building consent.
Key points to confirm with your council:
- Whether building consent is required for your specific situation
- Minimum setback distances from boundaries, buildings, and water sources
- Soil percolation (absorption) test requirements
- Whether a resource consent is needed under the Resource Management Act
Can You Physically Dig the Soakhole Yourself?
The physical excavation — actually digging the hole — is not restricted work in itself. A competent homeowner with the right tools (a spade, post-hole borer, or hired mini excavator) can dig the pit. However, there are important practical considerations:
- Call Before You Dig: Always contact Dial Before You Dig or your local utility providers or your local utility providers to locate underground services before excavating. Striking a gas line, water main, or electrical cable is extremely dangerous.
- Soil assessment: The soakhole must be sized correctly for your soil type. Clay soils drain poorly and may make a soakhole ineffective or cause surfacing of wastewater, which is a health hazard.
- Depth and lining: The design must keep greywater well above the seasonal water table and away from any bores or streams. BRANZ provides guidance on good building practice for drainage systems.
- Structural safety: Excavations deeper than 1.5 metres can be dangerous and may require shoring. Refer to WorkSafe NZ guidelines on excavation safety before digging.
What Is Restricted (Licensed) Work?
This is where the rules are firm. Under the Plumbers, Gasfitters, and Drainlayers Act 2006, connecting any plumbing or drainage to a greywater soakhole is restricted work that must be carried out by — or under the supervision of — a licensed drainlayer or registered plumber. This includes:
- Connecting the soakhole to your household drainage pipes
- Installing any inspection chambers or junctions
- Diverting existing waste pipes to the soakhole
The Plumbers, Gasfitters and Drainlayers Board (PGDB) oversees licensing in NZ. Doing this work yourself (or hiring an unlicensed person) is illegal, can void your home insurance, and may result in fines. Always ask your tradesperson for their licence number and confirm it on the PGDB register.
Healthy Homes and Rental Properties
If the property is a rental, greywater systems must also comply with the Healthy Homes Standards, which include requirements around drainage and moisture. A poorly designed soakhole that causes damp or surfacing wastewater could put you in breach of your obligations as a landlord.
Practical Steps for Homeowners
- Contact your council — confirm consent requirements and any local rules before doing anything.
- Engage a licensed drainlayer — get them involved early so the design meets Building Code requirements.
- Arrange a soil percolation test — this determines the correct size and depth of your soakhole.
- Apply for building consent — your drainlayer or a Licensed Building Practitioner (LBP) can help prepare the application.
- Dig the hole — once consent is granted and services are located, you may be able to do the physical digging yourself to save cost.
- Have the licensed tradesperson complete all plumbing connections and arrange inspections.
When to Call a Professional
You should engage a licensed drainlayer for any greywater soakhole project — this is not optional for the plumbing connections. If your site has complex drainage, high groundwater, or is near a waterway, you may also need a geotechnical assessment or an engineer. Find qualified local excavators and drainlayers on tradedirectory.co.nz who can assess your specific site conditions and guide you through the consent process.
Licensed Building Practitioner (LBP)
