Rainwater Tank Installation Adelaide: Sizing, Rules and Plumbing In

What South Australia requires of a rainwater tank

Since 2006, new houses in South Australia have had to include an additional water supply beyond the mains, and in practice that has almost always been a plumbed rainwater tank connected to at least one of 3 things: a toilet, the water heater, or a cold water outlet in the laundry. The specification sets both a minimum stored volume and a minimum area of roof feeding it, so a token tank hung off a carport gutter does not satisfy it. Check the figures current for your build, because they are the numbers your certifier will use.

What trips people up is the boundary between what anyone can do and what has to be done by a licensed plumber. It is not about the size of the tank.

• A tank on its own base with a gravity tap for the garden is not notifiable plumbing work.
• Connecting the tank to any fixture inside the house is licensed sanitary plumbing work.
• Any mains top-up arrangement is licensed work, because it creates a potential path from tank water back into the drinking supply.
• The overflow has to run to a legal point of discharge, which is a plumbing connection, not a hole in the garden.

Sizing a tank against real Adelaide rainfall

Yield is arithmetic. Multiply the connected roof area in square metres by the annual rainfall in millimetres, then by about 0.85 for what is lost to first flush, splash and evaporation. The answer is litres per year. Adelaide on the plains averages roughly 530mm, Stirling and the higher Hills run closer to 1,000mm, and Mount Barker sits between the 2.

The annual number is the wrong number to design against, and it is where most tanks get sized badly. Adelaide takes the bulk of its rain from May to October and then goes months with almost nothing. Storage does not have to hold a year of supply. It has to bridge the dry gap, and in a bad year that gap runs past 4 months.

Match the tank to the catchment first, then to the demand. A large tank fed by a small roof never fills.

When the tank is the whole supply: the Adelaide Hills

Across parts of Upper Sturt, Crafers, Aldgate, Bridgewater and the smaller settlements beyond, there is no SA Water main to connect to. The tank is the water supply rather than a supplement, and that changes every decision about the installation.

• Redundancy matters more than capacity. Multiple tanks manifolded together keep the house running while one is cleaned, repaired or isolated.
• The pump becomes critical equipment. Dry-run protection, a non-return valve and a sensible location are not upgrades here, they are the difference between having water and not having it.
• Frost gets underestimated. Exposed pump housings and pipework in the higher Hills need lagging, or the first cold morning becomes a call-out.
• Water quality management falls to the owner: gutter mesh, a first flush diverter, screened inlets and overflows, and a desludge every few years.
• Carted water needs a fill point a truck can reach, which is a decision for when the tank goes in rather than for February.

Bushfire requirements sit over the top of all of it. In a designated bushfire prone area, a development approval commonly requires a dedicated firefighting supply: a volume held in reserve so household use cannot draw it down, above-ground pipework and fittings that will not melt, and an outlet the CFS can connect to, which in South Australia means the 64mm male camlock, sited where an appliance can reach it. Your own approval conditions set the exact figures, so read them before choosing a tank rather than after it is craned into position.

The distance is real and worth being honest about. Nairne, Woodside and Mount Barker are a genuine drive from the Westbourne Park base, not a 10 minute run. Marc confirms an arrival time by text before setting off, so you are not losing a morning to a window.

What a compliant installation includes

The tank is the least interesting part of the job. Everything that decides whether it works for 20 years sits around it.

• A base that carries the load. A full 5,000 litre tank weighs over 5 tonnes on reactive Adelaide clay that moves seasonally, so it wants compacted crusher dust to specification or a concrete pad, level and drained.
• Screened inlets and overflows plus a leaf guard. An unscreened tank is a mosquito nursery within a fortnight.
• A first flush diverter, which dumps the initial dirty run off the roof before it reaches the tank. Essential on a drinking supply, worthwhile either way.
• An overflow taken to the legal point of discharge, not spilled at the base of the tank. Repeated saturation beside footings on reactive clay is how a tank causes cracking.
• A pressure pump matched to the demand, with dry-run protection, sited where the noise is not a nightly argument with a neighbour.
• An automatic mains changeover device where the house also runs on the mains, set so the tank is used first.
• Identification of tank-supplied pipework and outlets, so nobody makes a wrong assumption in a decade.

Rainwater is soft and slightly acidic, which is why it is pleasant to drink and easy on a kettle. It is also mildly aggressive toward copper, and in a house running entirely on tank water the tell is blue-green staining in basins and baths. Maintenance beyond that is short: clear the gutters before winter, check the first flush diverter drains down, and have the tank desludged every 2 to 3 years.

Retrofitting a tank to an older Adelaide home

Inner-suburban blocks in Goodwood, Unley, Black Forest and Cumberland Park throw up the same constraints every time: narrow allotments, side passages barely wide enough to walk, downpipes in the wrong places, and a rear yard that is largely paved.

• Slimline tanks solve the side passage. A tank 400mm to 600mm deep takes the space a garden bed was using, and 2 or 3 plumbed together beat 1 round tank that will not fit.
• A charged, or wet, system carries water underground from remote downpipes and back up into the tank inlet. It has to be watertight, needs a flush point at the low end, and the inlet has to sit below the gutter line to work at all.
• Underground tanks cost several times the same storage above ground once excavation into Adelaide clay, a crane and a pump are counted.
• Check setbacks, height and any character or heritage overlay before ordering. Finding out at delivery is an expensive way to learn it.

When a plumbed tank is not worth the money

This section costs us work and it belongs here, because a tank sold to the wrong house is an expensive ornament.

• If the goal is a lower water bill on a mains-connected suburban block, a fully plumbed and switched system takes decades to repay. The savings are real and they are small, and the supply charges do not move at all.
• If the only use is a vegetable patch and some pots, a tank on a stand with a gravity-fed tap does the whole job. No pump, no switching device, no plumbing connection.
• If the roof feeding it is a carport or a small extension, the tank will never fill, and a smaller tank properly connected to the main roof is the better buy.
• If an underground tank is being proposed and there is a spare 2 metres of side passage, price the slimline option first.

The honest reasons to install one are good ones: a garden that survives a hot dry summer, a build that requires it, a Hills property with no main, or a bushfire supply that has to be there whether it saves money or not.

Questions we get asked