Harvesting rain: a practical guide to garden water systems

Australia is the driest inhabited continent on earth, and the average backyard in a town like Dubbo, Bendigo or Bunbury can lose thousands of litres of precious water each year simply by letting rain run off the roof and disappear down the kerb. Gardeners who pay attention to their local climate know that the trick is not waiting for a downpour but capturing the steady soaking rains that arrive in autumn and the sudden cloudbursts of summer. With a thoughtfully designed catchment, even a modest house roof can keep a vegie patch, a few chooks and a stand of fruit trees going through the dry months. Learn more about Thesunshinethiryblog.com.

A rainwater system is one of the most forgiving projects a home grower can tackle. Most of the components are sold at the local Bunnings or a rural supply store, the parts screw together with a shifting spanner, and the whole thing can be expanded gradually as the garden grows. The biggest decisions are about size, placement and rules, because every shire has its own expectations about tanks, screening, and what happens when stormwater crosses a property boundary.

A bit of planning before the first poly tank arrives on the back of the ute will save hundreds of dollars and a lot of heavy lifting later. The notes that follow walk through sizing, choosing a tank, putting the pipework together, deciding on a pump, and the small print about Australian rules and rebates. Readers who are also keeping poultry will find a useful nod here toward the practical guides over at the homesteading site, which covers related tasks like setting up a chook run that complements a garden watering routine.

Sizing your system to suit the climate

The first real number to pin down is how much rain actually falls on the roof in a typical year. The Bureau of Meteorology publishes long-term averages for thousands of stations, from Cairns to Albany, and entering the closest postcode in their climate data viewer will give a rooftop figure in millimetres. A square metre of roof catches roughly one litre for every millimetre that falls, so a 200 square metre roof in a town that receives 600 mm of rain each year will yield about 120,000 litres if every drop is caught. In practice, between ten and twenty percent is lost to splash, the first flush, and overflow, so a more realistic working figure sits closer to 100,000 litres.

The second number is how much the garden will actually drink. A small vegie bed under a drip line uses a fraction of what thirsty lawn demands, and fruit trees with mulch beneath them can survive on surprisingly little. Recording the metres of hose used in a week during February, then multiplying by the number of summer weeks, gives a working estimate of peak demand. Pairing that demand against the BOM average shows whether one 5,000 litre tank will do the job or whether two or three linked tanks make more sense.

In many regions the rainfall curve is not even across the year. Perth's winter-dominated pattern is very different from Brisbane's summer storms, and a grower in the Adelaide Hills will plan for a slow, gentle soak that fills the tank over months rather than days. Matching tank size to the gap between wet seasons is what keeps plants alive in February, and it is more useful than any rule-of-thumb about tanks-per-bedroom that appears in glossy brochures.

Choosing a tank that suits the block

Aussie backyards are most often paired with poly tanks, which are the round or slimline plastic cylinders that dominate the landscape from Tasmania to the Top End. They are light enough to cart home on a small trailer, they do not rust, and the food-grade versions carry a list of approvals that council inspectors accept without argument. Slimline tanks in the 2,000 to 5,000 litre range tuck neatly down the side of a fibro house, while the squat round models sit happily on a sand pad near the back fence.

Concrete tanks earn their keep in bushfire-prone areas, where their mass helps them survive radiant heat, and they keep water cooler through long, hot summers. The downside is weight, which often calls for a crane and a reinforced slab, and the price, which is usually two or three times that of an equivalent poly unit. Blueline and Kingspan-style steel tanks sit in the middle on cost, last well in coastal regions with the right coating, and are commonly seen on the larger holdings of the Riverina and the Murray-Darling plains.

Whatever the material, three details deserve attention before purchase. The inlet strainer needs to keep mosquitoes and leaves out, because the same mozzies that pester the back patio will treat an open tank as a personal swimming pool. The overflow must be plumbed away from the slab so the foundation does not turn into a wading pool during a January deluge. And a sturdy, childproof lockable outlet near the bottom of the tank makes the difference between a daily chore and a quick turn of the tap on a forty-degree arvo.

Gutters, mesh, and the first flush diverter

The guttering already on the house does most of the heavy lifting, but it is worth spending an afternoon on the eaves before the new tank is plumbed in. A simple gutter brush or a length of fine leaf-guard mesh dropped into the trough keeps the worst of the gum leaves and the seed pods out of the downpipe. In a place like the Blue Mountains, where stringybarks shed bark all year, the difference between screened and unscreened gutters is a tank full of black sludge by March.

A first flush diverter is a small device that hangs off the downpipe and dumps the first ten or twenty litres of rain from each event. That initial water carries the dust, bird droppings and metal residues that have built up on the roof since the last shower, and sending it down the driveway rather than into the tank noticeably improves the smell and the clarity of the stored water. The diverter is automatic, needs a quick rinse every couple of months, and costs less than a decent pair of work boots.

From the cleaned downpipe, water travels through a sealed PVC or polypipe run to the tank inlet. A smooth fall along the pipe, with the occasional flush point, stops sediment building up at the low spots. Many installers leave a small inspection tee near the tank so the owner can see at a glance whether leaves or possum mischief are causing a blockage, and the same tee can be fitted with a tap for filling a watering can without dragging the hose out.

Pumps, irrigation and the wet end of the system

A garden that relies on gravity alone is a garden that lives in a hole or on a slab built up above the tank. In most suburban blocks, the tank sits low and the tap sits high, which means some form of pump is needed to move water at a useful pressure. A small 12-volt or 240-volt pressure pump the size of a shoebox is enough for a few drip lines and a trigger nozzle, while a larger household unit will feed a retic system, a washing machine and a stock trough without raising a sweat.

Drip irrigation is the quiet hero of the whole setup, because it delivers water at the rate soil can actually absorb it. Laying 13 mm poly drip line with in-line emitters spaced every thirty centimetres, snaked through the vegie beds and under the fruit trees, means the tank empties slowly and the plants drink deeply rather than getting a daily sprinkle that evaporates by lunch. A simple battery-operated tap timer, the kind that clips onto a standard 25 mm garden tap, takes the guesswork out of watering during a long, hot stretch when the gardener is busy elsewhere.

Anyone running geese or a small flock of ducks will quickly notice that birds and gardens share a thirst. Linking a small dedicated tap near the poultry pen to the same pump keeps the water bill down and the birds happy, and the same system can be used to flush a compost heap or top up a worm farm. Readers who are working on training your geese will already know how much water even a handful of birds can drink, and a tap on the tank is far more reliable than a bucket carried from the laundry.

Rules, rebates and bushfire considerations

Council rules around rainwater tanks vary more than the climate itself, and a quick call to the local planning office before the first trench is dug can spare a lot of headaches. In parts of New South Wales and Queensland, new houses are required to install a tank of a minimum size tied to the roof area, and the plumber who signs off the build will need to see an approved fitting on every inlet and overflow. Tasmania, Victoria and South Australia have their own lists, and heritage overlays in inner suburbs often add a layer of approval even for a slimline tank against a period wall.

A handful of state and federal rebates help with the upfront cost, particularly when the tank is paired with a pump or is being installed in a drought-affected region. The federal Water for Farm program, several state-level rain tank rebates, and the occasional council top-up have all reappeared in recent years after dry summers. Reading the fine print matters, because most rebates demand a licensed plumber, a plumbed connection to the garden rather than a simple hose, and sometimes a Smart Approved WaterMark stamp on the fittings.

Bushfire is the one issue that turns a simple project into a planning exercise. In a BAL-12.5 to BAL-40 zone, the standards call for metal mesh over every opening, screened ventilation on the tank roof, and a shutoff valve that can be closed before a fire front passes. A poly tank will generally survive low-intensity radiant heat, but a concrete tank is the safer bet where the ember attack is severe. Sitting the tank clear of the house, with a three-metre gap to any fence or shed, also helps the crew defend the property without tripping over a fitting in the dark.

A working rainwater system quickly becomes part of the rhythm of the household, as familiar as the kettle and the back door. Checking the leaf-guard before the autumn break, watching the gauge climb after a passing thunderstorm, and topping up the worm farm from the kitchen tap all become small satisfactions. The best reward is the first dry February when the garden is still green, the chooks are still laying, and the mains tap has barely been touched since October.