Two years, three house plans, one wastewater partner
The owners of a rural block in the Waitākere Ranges, West Auckland, spent more than two years waiting on their modular home, while the plans kept changing. WaterFlow stayed with them the whole way, checking in every couple of months and redesigning their NaturalFlow wastewater system three times at no extra cost, until it was finally installed in November 2023.
The challenge: a house that kept changing
The owners had a beautiful sloping block of just under three hectares in the Waitākere Ranges, bordered by native bush. They were already living on site in a cluster of small cabins: a bedroom cabin, an office, a work cabin with a loft and a storage cabin. None had a toilet or shower, and drinking water came from rainwater tanks.
The plan was simple: add a compact modular home with a proper kitchen and bathroom. Getting there was not. The home supplier's plans and timeline changed again and again, and the build was delayed for well over a year. Every time the house changed, the wastewater design had to change with it.
The site also sits within the Waitākere Ranges Heritage Area and next to a Significant Ecological Area, so any wastewater system had to protect the bush, streams and groundwater around it.
Our approach: one site, three designs
WaterFlow first visited in July 2021 for a full site assessment. Two bore holes to 1.2 metres found 200 mm of topsoil over silty clay loam, a Class 5 soil that drains moderately to slowly, with no sign of groundwater. The north-facing slope ran at 13 to 17 degrees, with no signs of instability.
That ruled out simple soakage and pointed to a NaturalFlow worm-based secondary treatment system, spreading treated water through surface-laid pressure-compensating dripline (PCDI) under mulch and planting.
Then the house kept changing, so the design changed with it:
|
Design |
House plan at the time |
Daily design flow |
Disposal field |
|---|---|---|---|
|
February 2023 |
New 2-bedroom home |
640 litres |
291 m² |
|
June 2023 |
2-bedroom + 1-bedroom homes |
960 litres |
436 m² |
|
July 2023 (final) |
1-bedroom home + 4 existing cabins |
1,280 litres |
512 m² |
Each version needed fresh calculations and updated plans. The first design was approved under a building consent from Auckland Council in July 2023, and the system qualified as a permitted activity under the Auckland Unitary Plan, so no separate discharge consent was needed.
The tricky bit: sticking with it
When a build stalls, it's easy for a project to fall through the cracks. WaterFlow made sure this one didn't:
-
Regular check-ins. The team got in touch every couple of months to see where the house was at, so the wastewater plan was always ready to move when the build did.
-
Redesigns at no extra cost. Every time the house plans changed, or new geotechnical feedback came in, WaterFlow updated the design free of charge.
-
Designing for real life. The final design counts the four existing cabins as sleepouts, sizing the system for 8 people rather than just the new home. The owners can keep using their cabins without outgrowing the system, and the NaturalFlow unit still has headroom, with a capacity of 1,600 litres a day.
The result
The NaturalFlow system was installed in November 2023, more than two years after WaterFlow's first site visit. The owners now have:
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A secondary treatment system sized for the whole site, treating up to 1,280 litres a day across a 512 m² dripline disposal field, with a full reserve area set aside for the future.
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Worm-powered treatment with no regular desludging. The worms in the Wormorator module reduce the volume of solids by around 95%, so there's no tank to pump out every few years.
-
A complete water setup. [CONFIRM: installed as quoted] Two 25,000-litre rainwater tanks buried 1 metre deep, a pressure pump, a drinking water filter, stormwater drains and a tank overflow, all from one supplier.
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Ongoing support. A free six-month check-up after commissioning, with six-monthly servicing recommended from there.
Project details
|
Location |
Waitākere Ranges, West Auckland (Auckland Council) |
|
Property type |
Rural lifestyle block, just under 3 hectares, rainwater supply |
|
Planning overlays |
Waitākere Ranges Heritage Area, next to a Significant Ecological Area |
|
Buildings served |
New 1-bedroom modular home, with 4 existing cabins allowed for |
|
Design flow |
1,280 litres per day (8 people) |
|
Treatment system |
NaturalFlow treatment, pumped discharge |
|
Disposal field |
512 m² surface-laid PCDI dripline, plus 100% reserve area |
|
Soil |
Class 5 silty clay loam, 13 to 17 degree slope |
|
Consent |
Building consent, Auckland Council (July 2023); permitted activity under the Auckland Unitary Plan |
|
Timeline |
Site assessment July 2021, three designs in 2023, installed November 2023 |
|
Design changes |
3, all at no extra cost |
|
WaterFlow team |
Dean Hoyle (design), Ken Hoyle (design review), Caleb Pirini (site assessments) |
Council-compliant, right across New Zealand
WaterFlow works with district and regional councils all the time. Our certified designers prepare the site and soil assessments, design reports and producer statements councils ask for, and our systems are designed to meet the New Zealand Building Code (G13/VM4) and AS/NZS 1547. With our head office in Maungaturoto and teams in Kerikeri, Auckland and Palmerston North, we know the local rules wherever you're building.
On this project, that meant a design that met Auckland Council's building consent requirements and the Auckland Unitary Plan's permitted activity standards, all within the protected Waitākere Ranges Heritage Area.
Planning a home on a rural block?
WaterFlow designs, consents, installs and services wastewater systems for rural homes and off-grid and remote properties across New Zealand. Learn how worm-based vermifiltration works, find out what a septic system really costs, or browse more of our projects.
Book a free site assessment and we'll help you plan your system, however long your build takes.
