Is a rainwater tank worth it?

The money, told straight

Mains water in Australia costs a few dollars a kilolitre. Even a big tank supplying the garden and toilets might displace 50 to 100 kL a year, which is a few hundred dollars. Against a few thousand for tank, pump and installation, payback on bills alone often runs a decade.

So if a spreadsheet is the only judge, a tank scrapes in slowly. The reasons most owners rate them sit elsewhere: what the water is like, what it lets you do, and what it protects you from.

Your garden prefers rainwater

• No chlorine or chloramine, which garden beds and soil biology notice.
• Naturally soft, so no mineral scale on leaves, pots or drippers.
• Close to neutral pH and free of the fluoride and salts that build up in some town supplies.
• Gardeners switching from mains commonly report the difference within a season, most visibly on seedlings and natives.

Water that’s yours

A tank keeps the garden alive through watering restrictions, waters stock and veggies through dry spells, and keeps toilets flushing when the mains has an outage. For rural and off-grid properties it’s not a nicety, it’s the supply.

There’s a quieter benefit too: you know exactly what’s in it, because you caught it. On town water you take what comes down the pipe.

The sustainability part, without the lecture

Every litre you catch is a litre the mains network doesn’t treat and pump to you, and a litre of stormwater that doesn’t rush off your roof into the street during a downpour. Multiply by a suburb and both effects are real. That’s why councils subsidise tanks rather than just approving of them.

Rebates and rules

Many councils and some states offer rebates on tanks, pumps and installation, commonly a few hundred dollars. Several states also require tanks (or another water-saving measure) on new builds and major renovations, so if you’re building, a tank may not be optional anyway.

Rebates change often and are council-specific, so check yours directly:

[your council name] rainwater tank rebate

Sizing one

The maths is friendlier than people expect: one millimetre of rain on one square metre of roof yields about one litre. A 150 m² roof in a 700 mm rainfall area catches roughly 100,000 litres a year, far more than most tanks can hold, which is why roundish numbers work fine.

As a guide: 2,000 to 5,000 litres covers a garden, 10,000 litres and up starts supplying the house, and rural properties relying on rainwater typically run 20,000 litres or more. Bigger is better value per litre, if the space exists.

The catch nobody mentions

Gravity from a tank outlet gives you almost no pressure. Half a metre of height is a twentieth of what your shower expects, so straight from the tap a tank delivers a dribble. Every tank that supplies more than a gravity-fed veggie bed needs a pressure pump, and the pump is what decides whether tank water feels like a compromise or like mains.

Budget for the pump when you budget for the tank, and the whole system lands the way the brochure implied.

The tank stores it. The pump delivers it.

A Grewa Boost draws from your tank and holds mains-like pressure through the house or garden, starting itself when a tap opens and standing by when it closes. The app shows the pump is healthy and lets you set the pressure you want, so the tank half of the system gets a delivery half that matches.

Common questions

How long does rainwater keep in a tank?

Indefinitely, if the tank is sealed against light and mosquitos and reasonably clean. Stored rainwater doesn’t expire; it just accumulates whatever falls in. Screens on inlets and overflows, plus a clean roof, matter far more than time.

Can we drink it?

Plenty of rural Australia does. Untreated tank water isn’t held to town-water standards though, so if you plan to drink from your tank, filter and disinfect it first. Our guide on making tank water safe to drink covers the setup.

Do I need council approval to install a tank?

Usually not for typical domestic sizes, but rules vary on placement, overflow connection and larger tanks. Your council’s website answers it in a few minutes, and any rebate application walks you through the requirements anyway.

What about mosquitos?

Screens on every opening, kept in good repair. A properly screened tank gives mosquitos nowhere to get in, and it’s a rebate and regulation requirement in most places.