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Rainwater Tanks: What You Need to Know

An Australian made rainwater tank and harvesting system can be an incredibly worthwhile investment. Capturing rainfall for personal use can help ease the strain on local reservoirs and reduce the cost of your water bills. There’s also that great sense of satisfaction that comes from being self sustainable and living off the land.

So, whether you’re looking to meet the requirements laid out by your local council or are ready to explore the possibilities of rainwater harvesting, here are some of the key benefits that come from installing a rainwater tank for water storage:

  • Reducing water costs
  • Having a backup supply of potable water in case of emergencies
  • Taking the strain off local reservoirs
  • Reducing the risks of flooding
  • Easing the strain on stormwater drains and sewers
  • Water restrictions workaround

It’s easy to overlook the benefits of a rainwater tank, especially when a seemingly endless supply of H2O is available to most via tap. However, a well implemented system can potentially reduce your dependence on mains water by up to 100%. Of course, it all depends on the frequency of rainfall and how the harvested water is used.

Indoors vs Outdoors Use

Using the water collected for gardening and washing the car is a no-brainer. But did you know that rainwater tanks can also be used for the washing machine, the hot water system, the toilet, and for drinking? A roof plumber can connect a tank to your faucets via a water pump so that it’s pressurised and can become a primary source of the water used throughout your home.

The Australian Government’s Department of Health reports that 10.1 per cent of Aussie households already rely on rainwater tanks as their primary source of water. The number jumps to a whopping 22 per cent if we’re just looking at South Australia.

Drought conditions can hinder a systems’ potential, and the rainwater does need to be treated to reduce the risks of bacteria and parasites. As rainwater is collected from your roof gutters, there’s a lot of potential for it to contain dirt, pollen and algae. So it’s essential to keep your gutters and roof plumbing clean and the tank chemically treated, especially if you plan on drinking the harvested rainwater.

A nifty device called a first flush diverter protects the cleanliness of your water supply by diverting the first flush of water. This potentially washes the dirt and other organic particles down the drain so that only the second cleaner rush of water ends up in the tank. A roof plumber or an experienced licensed plumber can handle the installation of the first flush diverter.

The collected rainwater can always be used exclusively in the garden and for washing the car with little to no treatment required.

blue steel rainwater tank

Types of Rainwater Tanks

With rainwater tanks becoming a standard feature of households in Australia, the choice of styles, size and materials continues to grow. The traditional round tank has given way to the slimline water tank better suited to suburban homes. A slim water tank is rectangular in shape and colour coded to fit alongside a house or fence. These storage tanks are commonly made from a tough polyethylene, but there are many material options to choose from. These are a few of the most common materials used in Australia:

Steel Rainwater Tanks

Steel tanks are made from corrugated or flat metal sheeting and come in many shapes and sizes. BlueScope Steel crafts a unique material called Aquaplate steel explicitly designed for tanks. It features a food-grade lining to protect your water quality and increase the life of the tank.

There are also galvanised and stainless steel options available. Galvanised tanks are more affordable than BlueScope Aquaplate but are at risk of rusting. Stainless steel is the answer to rust, but this material is by far the more expensive steel option.

Polyethylene (Poly Water Tanks)

Poly water tanks are popular for their affordability and non-corrosive materials. Reputable brands produce these tanks from food-grade polyethylene (plastic) which meets Australian standards for drinking water.

Poly tanks are commonly manufactured in one piece with no joints or seals, reducing the risk of leaking. They are often built rigid but are also available as a bladder tank, ideal for concealment in tight spaces like under the house.

Fibreglass Rainwater Tanks

Before polyethylene became the standard material, there were fibreglass tanks. Modern fibreglass tanks are made from more hygienic materials than the classics. Glass Fibre Reinforced Plastic is the technical name for the modern material which is more resistant to damage and heat.

Fibreglass or fibre reinforced plastic tanks are more lightweight than plastic tanks but are also stiffer and more prone to damage. The plus side is that fibreglass can be easily repaired. These days fibreglass tanks are commonly found on rural properties or reserved for commercial use.

Concrete Water Tanks

Concrete tanks are commonly reserved for farms and industrial sites, and they can be buried underground to save on space.

Concrete tanks can be custom built on site or manufactured and shipped out like other tanks. Concrete is a more expensive material than steel or plastic, although the contained water will always stay cool and these tanks are far sturdier. A below ground tank can sound appealing but do consider that extra work will be required to excavate the land and connect the tank for rainwater harvesting.

While on the topic of concrete, all rainwater tanks require a concrete slab on level ground to function as the base. SA Water stipulates that the slab should be a minimum of 150mm thick with no movement joints. Note that the regulations vary from state to state and that a bladder tank may not require the concrete slab.

white poly rainwater tank

What Size Water Tank do you Need?

Residential rainwater tanks are available with a wide range of capacities. For example, Bunnings water tanks start at just 100 litres water capacity and range right up to 22,500 litres. The 1,000 litre tank is amongst the most popular sizes for suburban homes and is a suitable capacity for gardening and a few other small jobs.

So, what size tank do you need? YourHome gives the approximate tank sizes required based on a four person household receiving evenly spread rainfall.

  • For flushing toilets and gardening: 2,000 – 3,000 litre capacity
  • For flushing toilets, washing clothes and gardening: 3,000 – 5,000 litre capacity
  • For providing a home’s entire water supply: 5,000 – 20,000 litre capacity

Consider that the larger the capacity, the more free space you will need. A 5,000 litre tank from Clark Tanks, in a slimline profile, measures 2.1m high x 3.3m long and 1.05m wide. This could take up substantial space if positioned at the side or back of a dwelling built on a small block of land.

How Much Rain Can You Collect?

A 5,000 litre tank doesn’t necessarily mean you will net 5k litres of rainwater. It needs to rain quite a bit for rainwater tanks to become a primary source for the home. Bushman Tanks says three factors influence the volume of water that you can harvest:

  • Area of your roof including the overhang
  • Maximum capacity of your tank
  • Annual rainfall in your area

Bushman Tanks provides the following formula for estimating how much you could capture:

Harvested water (L) = catchment area (m2) x rainfall depth (mm)

Multiply the area of your roof by the depth of rainfall using a rain gauge, and you will have an approximate measurement of what you can harvest. The Bureau of Meteorology is your best source regarding historical rainfall data in your area. Of course, the rainfall is different each year, which is why the formula can only be used to obtain an estimate.

Rainwater Tank Prices

The price of rainwater tanks will always depend on their size and materials. A polyethylene tank with a slim profile and 1,000 litre capacity will cost around $900 while a 5,000 litre tank costs upwards of $2000.

A BlueScope Aquaplate tank in a 1,000 litre capacity costs around $1,500 while a 5,000 litre steel tank goes for $2,500. Consider that these prices are limited to the tanks alone. The delivery of a system, its installation, the purchase of water tank pumps and roof plumbing can incur additional costs.
Apart from Bunnings, most retailers including Bushman Tanks, Kingspan and Clark Tanks require you to submit a quote before they will give you a fixed price.

rainwater tanks and gutters

Rainwater Tank Rebates

Rainwater tank rebates differ from state to state and from council to council. Regions of Western Australia are eligible for an Australian Government $1,000 rebate on the purchase of a new tank with further cash incentives for plumbing the tank or upgrading an existing system. Head over to QLD and Western Down’s residents are eligible for rebates up to $1000 on new tanks only. Rebates are always changing across the country, but it can certainly pay to do your research.

DIY Tank Installation

Anyone can head down to Bunnings to purchase a small tank and a few bags of cement for the slab. However, connecting the tank up to your faucets and the stormwater drain requires an expert.

A roof plumber should be your go-to for all plumbing work above and below ground. If the tank is only to be used for the garden, it’s possible that you can DIY. For everything else. It’s best if you leave it to the professionals.

Are Rainwater Tanks Worth it?

Absolutely! That’s precisely why most councils make rainwater tanks mandatory for new homes and those located in bushfire prone areas. You can have your own renewable source of water without much hassle, ultimately saving you money and lowering your impact on the environment. And if you’re taking advantage of rebates, a tank, pump and installation could cost you next to nothing.

Before you make a purchase, it’s recommended that you look into the local regulations regarding the quality of drinking water and tank placement. The last thing you want to do is buy a tank and then learn that the Building Code says it’s too big for your block.

Drought conditions may dissuade you from purchasing anyhow. But when the skies do open, you could very quickly discover that there’s a lot to like about rainwater tanks and harvesting systems.