Living in a high-risk area for bushfires, I've always been mindful of keeping the garden well-watered, and for 20 years the lush leaves of low-flammable plants and green lawn formed the primary protection for our house. Then, several years ago, we installed a bushfire sprinkler system, petrol pump and a 20,000L rainwater tank on our suburban-sized block. It wasn’t worth plumbing it to the house, we thought, not least because it had to be kept full right through the dry season, and with plentiful cheap mainswater available the garden would still be fine.
But of course, all that has changed with global warming, drought and water restrictions. Early this spring, like tens of thousands of other homeowners around Australia, we installed additional 6,000L tanks, plumbed into the house (but also available for the garden!) and connected to the fire-fighting tank so we could use the extra water during winter. Of course, the time to install rainwater tanks in temperate regions is BEFORE the autumn rains and, with some tank manufacturers running on 24-hour shifts with 3 month waiting lists, you should be ordering your tank now if it is to be useful.
People around Australia have been drinking from rainwater tanks since settlement and, despite the horror stories, you will not catch nasty 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 toilet (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 will even extend the life of your hot water service!
My mate Dave the plumber gave me lots of helpful advice on buying, placement, installation and maintenance. Here are his tips for getting it right.
1. How is the water to be used?
In the house? garden? both? This will determine how much storage you’ll need. It will depend on the size of your roof (catchment area), your local rainfall (amount and the way it falls over the course of a year), the number of people in your house, and – for gardeners – the size and nature of your garden and microclimate. State water authorities provide guidelines for calculating the size of tank you’ll need for your household needs for particular areas (see weblinks below), with less required if you have installed water-saving measures such as dual-flush loos, front-loading washing machines, low-flow shower heads etc. Alternatively, consult your plumber or tank manufacturer. Government rebates generally require a minimum size of tank, so check this too if you’ll be applying to a scheme.
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 can be tricky. The answer is to divide the storage volume by the total price; include delivery charges, stands etc, to get the cost per litre. All other factors being equal, 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. Other considerations might include requirements for 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 require 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). Tank stands over a certain height must be bolted to the concrete or wall (check with your tank manufacturer).
Of course, adding tanks to established homes can limit choice of size and location for your tank – you’ll need to consider foot and vehicular access. For many homes, slimline and modular tanks are an excellent option (but slimline tanks are relatively expensive). Bladders placed 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 held off installing a tank for many years for this reason, only to discover that, for about $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!
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 at all 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 am not looking forward to it.
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 allow soil or leaves to accumulate so that water channels between your waterproof membrane and the bottom of the tank. Some builders will make a base that is very slightly domed in the middle to aid drainage.
5. Plumbing, Pumps and Extras
You’ll need a licensed plumber if you’re connecting a rainwater 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 (in fact, if you’re applying for a rebate, keep all your paperwork).
Pressure pumps come in a range of sizes and qualities. You’ll need 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 together (that "ouch" factor under the shower!) Your plumber will advise on what size pump you’ll need. 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 will extend its longevity and prevent the motor burning out if the tank is emptied. 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.
Our tanks are plumbed to be switched manually between mainswater and rainwater - it’s a 30-second matter of switching off the mains, turning a valve, and switching on the pump – but automatic switching systems are available 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 may be less attractive to gardeners, who will want to use rainwater in their garden.
First flush systems that divert the initial flow from gutters are excellent but must be scrupulously maintained and emptied regularly, as they can incubate bacteria and exacerbate contamination of tanks. 5 micron carbon filters installed between the tank and house will 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.
All tank openings should be screened to prevent the ingress of frogs, mice, small birds etc, with mosquito-proof mesh grill plates over inlets.
What are you Waiting For?
Sustainability is the catchcry of today, and becoming self-sufficient in water is a big plus not just for you, but for the environment. And for gardeners, you can keep those vegies, pot plants and treasures alive, completely guilt-free!
