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Off-grid power, water and wastewater for tiny homes

From Modular Living Australia — the independent knowledge base Last updated: 31 Jul 2026

Going off-grid is usually described as a way to avoid the system. It is not. An off-grid tiny home still needs approvals, still needs licensed trades, and adds a set of standards that a connected dwelling never encounters. What it buys is independence from the mains and, on a remote block, a lower total cost than trenching services in. This guide sets out what each of the three systems actually requires and which of them decides whether a site works at all.

Off-grid is not outside the approval system §

Council approval may still be required for an off-grid tiny home depending on how it is used and where it is located, and a home intended for permanent living will generally need approval as a Class 1 dwelling meeting local planning and building requirements. The off-grid systems themselves — water storage, wastewater treatment and power generation — may also need to meet specific standards^[1].

New South Wales illustrates how the pieces divide. Domestic solar arrays and rainwater storage tanks generally qualify as Exempt Development under the State Environmental Planning Policy (Exempt and Complying Development Codes) 2008 where basic structural sizing rules are met. On-site sewage management systems, including septic tanks and composting toilets, must be designed in accordance with AS/NZS 1547 and are approved, inspected and licensed exclusively by the local council under section 68 of the Local Government Act 1993 — the NSW Environment Protection Authority does not issue operational permits for domestic single-household setups^[2].

That division is the shape of the problem generally: power and rainwater are usually the easy part, and wastewater is where the approval work sits.

Power: sizing is the whole problem §

There is no useful published rule of thumb for solar sizing on a tiny home, because the answer depends entirely on the appliances and the occupants. A local solar installer is best placed to assess the expected load and kilowatt-hour consumption and to size a system with redundancy for cloudy days and night-time use^[3].

The design constraint that catches people is seasonal rather than average. A system sized on annual average generation will fail in the shortest, cloudiest fortnight of the year — which is why the specification should target seasonal loads rather than a yearly figure^[4], and why winter conditions are the sizing case^[5].

The specification sequence a builder should be able to produce covers the solar array, battery capacity and inverter selection, a decision on whether a backup generator is included and how a compliant changeover arrangement is provided, and then the wiring, protection devices and commissioning documentation^[4]. The last item matters more than it sounds: an off-grid electrical installation without commissioning records is difficult to insure, service or sell.

Water: how much, and from where §

A single person typically uses 50 to 100 litres per day in a tiny home, and a 10,000 litre rainwater tank is described as providing a good buffer for most regions^[5].

Those two figures give a usable first pass. At 100 litres per day, a 10,000 litre tank holds roughly 100 days for one person and about 50 for two — before any allowance for a dry spell, which is what the buffer is for. Roof area and local rainfall determine whether the tank refills fast enough, and that calculation is site-specific.

Making tank water safe to drink is a separate system. Filtration is needed to keep debris out and, where disinfection is wanted, a UV filter costs approximately A$2,000 with a plumber installation of A$250 to A$500; filter cartridges should be replaced every 6 to 12 months and the ultraviolet lamp every 12 months^[3]. A pump is required to move water from the tank into the home^[3].

Those replacement intervals are the part most often forgotten. A UV system with an expired lamp provides no disinfection while continuing to look like it works.

The full water specification should cover tank sizing, filtration and UV specification, and backflow prevention^[4].

Wastewater is the part that decides the site §

If a site is going to fail, this is usually where.

For a flush toilet, a blackwater treatment system is required; compact on-site biodigesters are available that can treat both greywater and blackwater for irrigation reuse^[6]. For a composting toilet, models should comply with AS/NZS 1546.2:2008^[6].

Separating blackwater from greywater is an option for strictly off-grid homes, but it requires a high level of user interaction and maintenance, and council approval for composting toilets and standalone greywater systems can be more complex and is often subject to strict environmental health assessments in New South Wales, Queensland, Victoria and Tasmania^[7]. Installing a wastewater system is not a do-it-yourself project^[7].

Greywater must never be released into lakes, creeks or oceans. A greywater system comprises the outlet pipe, a filter, a grease trap, slotted pipe and a gravel trench before the water seeps into the garden, and local council approval may be required to install one^[8].

Three practical consequences follow.

• Soil and site constraints come first. The wastewater pathway has to suit the soil and the site, not the other way around^[4] — which means a soil assessment belongs before equipment selection, not after.
• A composting toilet is a maintenance commitment, not a shortcut. The approval may be harder than for a conventional system, and the ongoing user involvement is real^[7].
• Cleaning products become a system component. Greywater destined for a garden constrains what can be put down the sink.

Bushfire §

Fire safety requirements apply in bushfire-prone areas^[5]. Where they do, off-grid planning should include a dedicated static water supply, metal fittings and safe access to support firefighting^[4].

This is one of the few places where off-grid design and compliance point the same way: a tank that already exists for domestic supply can serve the static water requirement if it is specified and fitted correctly, and cannot if it is not.

Documentation at handover §

The handover pack should include product warranties, manuals and maintenance schedules for every system^[4].

For an off-grid home this is not administrative tidiness. The systems have service intervals — filter cartridges, UV lamps, battery maintenance, wastewater servicing — that nobody will remind the owner about, and the documentation is what an insurer, a future buyer or a service technician will ask for first.

What is not covered here §

This guide does not specify system sizes, and no Australian standard or government guidance on solar sizing for tiny homes has been located for these purposes; sizing is a job for a licensed installer working from the actual load.

Also not covered by the sources compiled here: gas installation and certification; battery chemistry and fire safety requirements; drinking water quality testing regimes; the approval pathways for on-site wastewater outside New South Wales, which differ by state and council; and system running costs over time. Product names and brands are deliberately omitted — this site does not recommend equipment.

References §