Is Storing Rainwater a Smart Move? What You Need to Know

Rainwater tanks used to be something you associated with farms and off-grid properties. These days they are a common sight in Australian suburbs, and for good reason. A tank lets you catch the rain that falls on your roof and use it for the garden, the car or even the toilet, which cuts your water bill and takes pressure off the mains supply. In a country with some of the highest water use per person in the world, and with cities that keep flirting with water restrictions, it makes sense.

But a rainwater tank is not a set-and-forget appliance. There are real questions about safety, water quality and whether the setup will pay for itself. Here is what to weigh up before you buy one.

Why people install rainwater tanks

The main reasons are water conservation, cost and a bit of independence from the mains.

Using rainwater for the garden, the lawn and washing the car saves the treated tap water for the things that really need it, such as drinking and cooking. That matters most during dry spells, when outdoor water use is often the first thing restricted. In cities such as Melbourne, where restrictions have been a regular feature of summer, a tank keeps the garden alive without breaking the rules.

There is an environmental angle too. Catching rainwater reduces demand on the municipal supply and lowers stormwater runoff, which otherwise carries pollutants into local rivers and bays. Every tank is a small buffer between a downpour and the drainage system.

And after the upfront cost, the water itself is free. How much you save depends on the tank size, how much you use outdoors and your local water prices, so the figures vary from house to house.

How safe is stored rainwater?

Rainwater is clean when it falls, but it stops being clean the moment it hits your roof. Dirt, leaves, bird and possum droppings, dust and chemical residue from roofing materials all wash into the tank with the first rain. Bacteria such as E. coli and Legionella can also find their way in, along with heavy metals if you live near busy roads or industrial areas.

That is why the general rule is simple: do not drink untreated rainwater. For watering the garden, washing the car and flushing toilets it is perfectly fine, and that is how most households use it. If you want to drink it, it needs proper treatment, and the Australian Drinking Water Guidelines set out what that involves. Filtration, UV sterilisation, chlorination or boiling can all make stored rainwater safe, but they add cost and maintenance, which is why most people keep the tank for non-drinking uses.

How to store rainwater safely

A tank is only as good as its setup, and a few habits make the difference between a useful water supply and a health risk.

Choose the right tank. Sizes run from small 500 litre tanks up to large ones many times that. Polyethylene, stainless steel and concrete are the common materials, and stainless steel is popular in places with strong sun because it resists UV damage. Whatever you choose, make sure it is opaque, because light encourages algae.

Keep the roof and gutters clean. Debris in the gutters ends up in the tank, so fit leaf guards and a first flush diverter, which sends the first, dirtiest water away from the tank after each rain. A fine mesh screen over the inlet keeps out insects and larger debris.

Filter the water before it enters the tank, and treat it if you plan to use it indoors. Simple mesh filters catch the big stuff, while multi-stage filtration handles finer sediment. For potable use, a UV sterilisation unit, chlorination or ozone treatment adds protection, and boiling remains the simplest fallback.

Maintain the system. Tanks need an annual clean to remove sediment, pipes and fittings need checking for leaks, and water quality is worth monitoring if you use it inside the house. None of this is difficult, but it needs to happen.

Rainwater tanks in Melbourne and Perth

The local climate shapes how useful a tank is. Melbourne averages around 650 mm of rain a year, but it falls unevenly, with dry summers that leave gardens thirsty. A tank there is most valuable for keeping outdoor watering going through the warmer months without pushing up the bill.

Perth gets slightly more, around 730 mm a year on average, but most of it falls in winter, and the summers are long, hot and dry. Tanks there are often sized to capture the winter rain and store it for summer use, which is why larger tanks are common. In both cities, many councils have offered rebates for tank installation as part of water conservation programs, so it is worth checking what is available in your area before you buy.

Is installing a tank worth it?

The pros are clear: less reliance on mains water, a buffer during restrictions, a genuine environmental benefit, possible savings on the water bill and added value to the property.

The cons are just as real. The upfront cost of a tank and installation typically runs from around $1,500 to $5,000 or more, depending on size and system. It needs regular maintenance, it will not make the water drinkable without extra treatment, and in a dry year there may not be enough rain to fill it. A tank is a tool that pays off over time, not an instant saving.

Questions people ask about rainwater tanks

Can you drink rainwater from a tank? Only if it is properly treated. Untreated rainwater is not recommended as a drinking supply under the Australian Drinking Water Guidelines, so most households keep it for outdoor and non-potable uses.

How big a tank do you need? It depends on your roof area, rainfall and how you plan to use the water. A small tank might cover the garden; a larger one can support toilets, laundry and outdoor use through a dry summer.

Do you need council approval? Rules vary between councils, especially for larger tanks or those plumbed into the house. It is worth checking local regulations before you install.

Will a tank save you money? It can, over time, by cutting mains water use for the garden and other outdoor jobs. The saving depends on your usage, rainfall and local water prices, so the payback period varies.

A tank only earns its place with the right setup

Storing rainwater is a sensible move for a lot of Australian households, especially in Melbourne and Perth where water conservation genuinely matters. It saves water, softens the blow of restrictions and gives you a bit of independence from the mains. But the tank is only half the story. It needs a clean roof, decent gutters, a first flush diverter and a filter, and it needs regular maintenance, or it becomes a health hazard instead of a water supply. Set it up properly, use it for the jobs it is good at, and treat the drinking question with the caution it deserves. Do that, and a rainwater tank is one of those quiet home improvements that pays you back every time it rains.

Sources: NHMRC, Australian Drinking Water Guidelines.