Before You Buy a Transportable Home: 10 Water and Wastewater Questions to Ask

01Question 1: What water and wastewater services are available at the property?

Start by confirming the available services and the proposed points of connection.

For a granny flat using the exemption, the availability and capacity of network services affect the servicing requirements. Ask the designer and provider to establish the relevant requirements for your property.^[1]

Ask who will obtain that confirmation and who will include the external connection work in the project.

02Question 2: Can the existing septic or treatment system accommodate another home?

An existing system should be assessed as a complete arrangement, including treatment and land application.

MBIE identifies wastewater loading, soil conditions and the capacity of the soakage treatment area as relevant considerations. Adding another dwelling also requires the applicable sewage-treatment rules to be addressed.^[2]

Request the existing system records and any consent conditions, then ask the wastewater professional to establish what can be retained and whether an upgrade is needed.

03Question 3: What occupancy and pattern of use will the design allow for?

Describe the intended household, not just the floor area.

Tell the project team about permanent occupants, regular visitors, laundry use, seasonal occupation and any realistic future change in use. Ask the designer to establish the appropriate design assumptions rather than relying only on who will move in first.

This is also the point to explain whether the home will be owner-occupied or rented, and who will manage routine servicing.

04Question 4: Which toilet arrangement suits the household and building layout?

Compare the proposed toilet options before the bathroom and foundations are finalised.

A waterless composting toilet is one possible sanitation approach. Building Code clause G1 provides for non-water-borne disposal through a healthy and safe disposal system; the selected product and installation still need to suit the project.^[3]

Ask for model-specific information covering intended use, capacity, ventilation, servicing and residual handling. For an underfloor arrangement, have the designer confirm the required space and access.

05Question 5: How will all the remaining household wastewater be managed?

Identify every source: shower, bathroom basin, laundry, kitchen sink and dishwasher where fitted. Then ask where each flow goes and why that arrangement has been selected.

Kitchen-inclusive treatment needs to be specified deliberately. WCTNZ®’s treatment-based arrangements include suitable grease interception and screening ahead of the greywater system where kitchen wastewater is included. An engineer-supported simpler diversion arrangement may be appropriate on suitable sites, but it is not an assumption that applies to every property.^[4]

06Question 6: Is there suitable land for the proposed wastewater discharge?

Where wastewater will be applied to land, ask the designer to identify the actual usable area.

Soil type, soil depth, wastewater volume and the relationship to waterways or flood-prone ground affect the suitability of a land-application arrangement. The receiving area is a functional part of the wastewater system.^[2]

Include it on the site plan alongside the home, access, parking and outdoor living areas. Ask whether a reserve area is required and what restrictions will apply to future use of that land.

07Question 7: Where will the home’s water come from?

Confirm whether the dwelling will use a network supply, an existing private supply or a new rainwater arrangement.

For rainwater, MBIE identifies rainfall, roof collection area, household use and the availability of another supply as factors affecting storage selection. Water intended for drinking and other household uses also needs appropriate treatment and maintenance.^[5]

Ask the designer or supplier to explain how the proposed system will operate through dry periods and how pumps, filters and treatment equipment will be accessed.

08Question 8: Do the floor level, drainage routes and access suit the selected equipment?

Have the building supplier and site-services team review the installation together.

Ask them to check the finished floor level, plumbing outlets, available drainage fall, proposed pumps, ventilation routes and access to equipment. Where the granny-flat exemption is proposed, have the designer verify its plumbing restrictions, including the restriction on pumped systems inside the dwelling.^[6]

For equipment needing underfloor space, request the manufacturer’s required clearances and confirm them on the drawings.

09Question 9: How will roof water, surface runoff and tank overflow be managed?

Give stormwater its own place in the plan.

Rainwater tank overflow needs a suitable route. Roof collection does not remove the need to manage overflow when the tank is full.^[5]

Ask the designer to show what happens during heavy rain, including runoff around the building and the relationship to any wastewater land-application area.

10Question 10: Who is responsible for installation, commissioning and ongoing care?

Before accepting the package, identify who is supplying the equipment, designing the arrangement, performing regulated work and confirming that the installation operates as intended.

For granny flats using the exemption, the required licensed professional involvement and completion documentation remain part of the process.^[7]

Request operating instructions, maintenance requirements and a clear support contact. Ask what the owner should do during a power interruption, equipment fault or service visit.

For a genuinely off-grid arrangement, the fallback cannot simply be described as “divert to sewer” when no sewer exists. The design needs a lawful way to manage those flows.^[4]