Helen McKerralTanks

South Australia is notoriously Aussie’s driest state and, though we’ve had two La Nina years, the previous decade of El Nino weather patterns had huge impacts on gardeners. Even as climate change sceptics point to eastern Australia’s floods, and the federal government declares the drought is ended, my rainfall gauge says that rainfall in these last two years in the Adelaide Hills has still been below average. 

My rainfall graph showing below average rainfall in the Adelaide Hills

More importantly, Adelaide has the longest dry period (that is, the longest average time between rainfalls) of any Australian capital city, and that’s highly significant for gardeners.

Adelaide home owners have always had rainwater tanks – when I was growing up, there was one in almost every back yard, before concerns about germs & disease reduced their numbers. Fortunately we’ve come full circle since then, with state law requiring all new houses to have a rainwater tank (albeit a pathetically small one).

Living in a high-risk bushfire area, I’ve always kept the garden well-watered, and for twenty years the lush leaves of fire-retardant plants and green lawn formed the primary protection for our house. Then, about eight years ago, we installed a bushfire sprinkler system, petrol pump and a 16,000L rainwater tank. It wasn’t worth plumbing into the house, we thought, not least because it had to be kept full right through the dry season, and with plentiful cheap mains water available.

But all that changed with drought and water restrictions. About five years ago we installed two galvanised tanks (totalling 5,000L), plumbed into the house (but also available for the garden!). Two years ago we added another three (totalling 5300L) to harvest from the new shed. All six tanks are interconnected for firefighting and use in the house &/or garden. We’ll add one more small tank (probably about 6,000 L) in the northwestern corner of the new block, adjacent to the shed, and later a tiny one of 500-1,000L by the woodshed. The latter won’t be for storage, per se, but to help redirect and distribute rainwater onto the lower native section of our new area, rather than letting it all run to the two huge radiata pines next door.

We added 3 tall steel tanks to harvest water from the shed

People around Australia have been drinking from rainwater tanks since settlement and, despite the horror stories, you won’t catch tummy wogs from a properly installed and maintained rainwater tank. If you’re still sceptical, you can use rainwater for everything but drinking: for washing (you’ll save on soaps and detergents!) and for the loo. Conversely, some folk have most of their house plumbed to the tank, but use mains water for the toilet because they don’t want to waste their lovely rainwater! Rainwater even extends the life of your hot water service!

My mate Dave the plumber gave me lots of helpful advice on tank buying, placement, installation and maintenance. Here are his tips:

1. How will I use the water?

In the house? Garden? Both? This determines how much storage you’ll need and depends on the size of your roof (catchment area), your local rainfall (amount, plus the way it falls over the course of a year), the number of people in your house, and – for gardeners – the size and style of your garden, and your microclimate. State water authorities provide guidelines for calculating the size of tank you’ll need for your household needs (eg

Smart Watermark, Planning South Australia, Sydney Water and Queensland Department of Environment & Resource Management. Government rebates usually require a minimum size tank, so check this too.

2. Cost, Shape and Materials

With a plethora of tank shapes (round, modular, slimline), materials (concrete, galv, aquaplate, colorbond, steel, fibreglass, poly, bladder) and sizes, comparing cost is tricky. The answer is to divide the storage volume by the total price (include delivery charges, stands etc), to get the cost per litre. You’ll be surprised at how much it varies. Overall, large tanks are generally cheaper per litre than small ones of the same type and, as you’d expect, one large tank is cheaper than two smaller tanks making up the same volume. Also consider longevity, available space and bushfire risk (no plastic tanks).

The cheapest option is a rainwater tank on a stand with gravity feed only; as soon as you need integration into the house you’ll be looking at pressure pumps, licensed plumbers, backflow valves and other expenses.

3. Location

Dave recommends that rainwater tanks always be installed as high as possible to maximise gravity feed options (eg gravity-fed sprinklers). Bolt tank stands over a certain height to the concrete or wall (check with your tank manufacturer).

Adding tanks to established homes often limits size and location options; modular and slimline tanks are excellent, though the latter are relatively expensive. Underground tanks, and bladders for under decking, are space-saving, too.

And there’s one more alternative for established homes with no access for a large tank to the back yard. We delayed installing a tank for many years for this reason, only to discover that, for just $150 extra, we could have a steel tank assembled on site, right in our back yard! We prepared the site, the workers arrived one morning, built the tank, placed it in position, and were gone by 4pm. Wonderful!

One of our many steel watertanks

4. Site Preparation

Get it right. I prepared the site for our bushfire tank myself and, though I used the correct materials (gravel, sand, dolomite and a waterproof membrane) I didn’t compact the base sufficiently. Now the tank has a lean – not dangerous, but it reduces the capacity of the tank and we’ve had to move the overflow pipe to the opposite, lower side. Re-levelling the base will be hideously onerous – we’ll have to empty the tank, lever it up in a cramped space, and somehow backfill underneath. I doubt it’s going to happen!

If the tank is on the ground rather than on a stand or concrete plinths, make sure that water drains away from the base, and don’t let soil or leaves accumulate so that water channels between your waterproof membrane and the bottom of the tank. A base that’s slightly domed in the middle aids drainage. Plastic tanks can go directly on the ground.

5. Plumbing, Pumps and Extras

You’ll need a licensed plumber if you’re connecting the tank to the house. In areas with mains water, backflow devices must be fitted, and there are various other regulations that apply regarding installation. You’ll receive a Certificate of Compliance from the plumber (if you’re applying for a rebate, keep all your paperwork).

Pressure pumps come in a range of sizes and qualities. Choose a more powerful pump for larger families, two storey homes, or ones with several bathrooms where, say, the washing machine, toilet and shower may operate simultaneously (avoid the “eeek” factor under the shower!). Your plumber will advise you. We bought a smallish but gold standard ‘Grundfos’ – more expensive than local products, but cheaper to run, quieter, and with stainless steel bits and an automatic cut-out switch that extends its longevity and prevents the motor burning out if the tank empties. Incidentally, some low-flow shower heads are incompatible with some pressure pumps, so check if you have one already installed. An electrician will need to install an external power point if you don’t already have one.

It’s also worth buying a pressure tank (aka an accumulator). These little tanks (usually between 8L-80L for domestic use) have a pressurised diaphragm inside, and are installed between your pump and the outlet to maintain pressure, so the pump doesn’t cut in every time someone washes their hands or a tap drips; you’ll save a lot of electricity.

My tanks are plumbed to be switched manually between mains water and rainwater – it takes 30 seconds to switch off the mains, turn a valve, and switch on the pump – but you can buy automatic switching systems that switch to rainwater for as long as there’s some in the tank, and only go to mains when they’re empty. This option is unsuitable for gardeners who want to save rainwater for irrigation during water restrictions.

First flush systems are excellent but must be scrupulously maintained, as some can incubate bacteria and exacerbate contamination of tanks. 5-micron carbon filters installed between the tank and house remove impurities, but they must be cleaned regularly too. As for reverse osmosis filters, Dave the Plumber reckons they’re overkill, and that too many minerals can be removed from the water. Of course, all tank openings should be screened to prevent frogs, mice, small birds etc, with mosquito-proof mesh grill plates over inlets.

You can fit in tanks almost anywhere, like these ones well hidden behind a screen

What are you waiting for?

Plenty of alternatives exist for retaining water on your property – I haven’t even mentioned on-site-retention basins, grey water recycling, reedbeds, surfacing options and swales, to name just a few, but rainwater tanks come in varieties to suit almost every budget and garden space. Becoming self-sufficient in water is a big plus not just for you, but for the environment – imagine how full Adelaide’s reservoirs would be, and how little stormwater runoff we’d have into the sea, if every household used rainwater, even if only during the winter months. No need for a desalination plant! And for gardeners, you can keep those vegies, pot plants and treasures alive, completely guilt-free!

(Daily Crafers data can now be found here but it gives me a good comparison between years at my house.)

For other Adelaide stations, go here and here

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Helen McKerral

About Helen McKerral

Horticultural journalist, photographer, contributor to many garden magazines, and author of 'Gardening on a Shoestring'. Adelaide Hills, South Australia

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