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Water falls Discover the bright side of wet weather, with our guide to storing rainwater to keep your garden lush

Do water restrictions mess with your plans for fabulous flowers and a verdant lawn? Solve the problem with a tank. “Harvesting rainwater can be a very effective, safe and renewable way of watering your garden during the dry spells that we inevitably experience,” says Chris Jenks, NSW key account manager at Clark Tanks and National Poly Industries. Which tank you choose will depend on various factors, such as how you intend to install it and what you want to use it for.

Size it up Mini tanks not connected to the mains can be installed DIY. Elevate them on compatible stands to make it easy to fill a watering can or supply a gravity-fed drip irrigation system. Council approval is not normally needed for rainwater tanks smaller than 10,000L, but check with your local water authority. For example, it may not be legal to install a tank over existing pipework, and you may need to install a backflow preventer.

“The biggest mitigating factor when choosing a water tank will be space,” says Chris. “For every square metre of roof space you have, each millimetre of rainfall will put one litre of rainwater in your tank.” 

Get connected Max out your available space by linking two or more tanks. “A level linking kit can be used with any small tanks,” says Aaron Gionis, sales manager at Maze. “The 100L Maze mini tanks and the Garantia range of tanks have an internal thread, so the connection fitting to the tank simply screws into them directly.” For larger tanks, you will need to assemble your own system. Include an isolating valve for each tank; if one of them springs a leak or gets contaminated, you can take it offline for repairs or cleaning without affecting the rest of your water supply.

Garantia ‘Classic’ 300L 2 in 1 zinc water tank in Grey, $598, I/N: 0013072 (plants not included)†

Chris Jenks Clark Tanks and National Poly Industries

1 National Poly Industries 1,000L round squat water tank in Mist Green, from $672, I/N: 4818304†. 2 Maze 300L rainwater mini tank, $149, I/N: 3130780. 3 Clark Tanks 2,000L poly slim water tank in Stormedge Blue, from $977, I/N: 4819456†. 4 Garantia ‘Linus’ 220L 2 in 1 water tank in Zinc Grey, $399, I/N: 0013083†. 5 Garantia 3,000L underground rainwater tank, from $2,595, I/N: 4813385†. See your local store to determine your tank range.

Maze 100L rainwater mini tanks, $72 each, I/N: 3130198 Maze water tank diverter, $15.54, I/N: 3130252

Maze rainwater tank stands to suit 100L tanks, $19.95 each, I/N: 3130203 Maze level linking kits, $29.95 each, I/N: 0087291 (links up to 3 tanks) Check your flow for size

Figure out your water consumption to find the tank size you need

1If you are using a hose or sprinkler, open the tap to achieve the same water flow as you normally use.

2Time yourself pouring water at this rate into a bucket or watering can for exactly 20 seconds, then shut off the tap.

3Measure how much water has flowed into the container during that time, then multiply it by three to find your flow rate. For example, if you have an 8L watering can that’s half full, your flow rate will be 4L x 3, so 12L per minute.

Knowing the flow rate you need will help you choose a suitable tank size. If your irrigation system is connected to a timer that switches on your sprinklers for five minutes a day with a flow rate of 12L per minute, it will take just over a month to go through a full 2000L tank. Heavy lifting A larger slimline tank with a capacity of 2000-3000L can be situated along the side of your house. Before installing a tank of this size, ensure that the location will be able to bear the weight of the full tank – every 1000L literally weighs a tonne! Your tank supplier will provide you with recommendations for a suitable substrate. A concrete slab, for example, should be strength rated at 25MPa (megapascals), and reinforced with F62 mesh (steel ‘reo’).

TOP TIP

For a small installation, a downpipe diverter might be all you need – it has an integrated screen to filter out debris from the gutter, and a built-in overflow that redirects excess water back to the downpipe

6 ClayTech Pumps ‘DiverTron C6’ submersible rainwater pump, $665, I/N: 4819844†. 7 ClayTech Pumps ‘EcoBoost 3’ rainwater pump, $299, I/N: 5104066. 8 Rain Harvesting 90mm overflow flap

Safety tip All plumbing and electrical work must be done by a licensed tradie

Pipe dream To fill a larger tank, or a linked series of tanks, it’s usually best to redirect your downpipe altogether. Install a first-flush diverter between your gutter outlet and your tank supply pipe to catch the worst of the gunk that washes off your roof when it starts to rain. You’ll also need an overflow pipe to allow rain to run back into the wastewater system after the tank is full.

valve, $13.90, I/N: 4761094. 9 Rain Harvesting 100mm first flush downpipe diverter kit, $67.37, I/N: 4779883† (clear pipe not included). 10 Maze moisture sensing irrigation kit, $89, I/N: 0087293. 11 Ozito 9 piece tank to pump installation kit, $20.55, I/N: 4819851. Some products are not available at all Bunnings stores, but may be ordered.

Watch this space A water tank needn’t be a dominant feature – highdensity polyethylene tanks can be manufactured to look like terracotta, zinc, stucco or other attractive materials. Decorative tanks are available in a range of shapes and finishes and can store up to a generous 300L. Some include a planting tray on top to help them blend into the garden. If you’re building a home from scratch or doing major landscaping, you might consider an in-ground tank. These are essentially invisible and take up no external space, while also preventing the growth of algae as they have zero exposure to sunlight.

The most common material for tanks is high-density polyethylene, which is durable and UV-resistant

Under pressure You’ll need a pump to bring tank water up to mains pressure. This will allow you to connect it to your irrigation system. The two main types available are submersible pumps, which are kept inside the tank itself, and external ones. An external pump may tend to be noisier, but is easier to access if you are upgrading your system and need to change connections or fittings.

If using an external pump, hook it up to your tank’s outlet tap with a flexible hose to absorb vibrations. The pump’s output can be connected to your irrigation system in the same way as you would connect an ordinary garden tap. ◆

Watch it! Work out how to use your harvested rainwater: bunnings.com.au/how-to-planan-irrigation-system