Rainwater Tank Installation for Canterbury Properties

Sizing the tank to your roof and use

Tank size depends on roof catchment area, average rainfall, and what the water is used for. A property relying on rainwater as its sole supply needs a much bigger tank and more careful budgeting for dry spells than one simply topping up garden and outdoor use.

As a rough guide, we work out expected annual roof yield from the catchment area, compare it to household demand, and size the tank to bridge the longest realistic dry stretch rather than an average year.

First-flush diverters

A first-flush diverter directs the initial run-off from a roof, carrying dust, bird droppings and debris, away from the tank before clean water starts flowing in. It's a simple, inexpensive fitting that makes a real difference to water quality, especially for drinking supplies.

We size the diverter to the roof area, since a bigger roof needs more first flush diverted before the water is worth capturing.

Council rules for rural Canterbury

• Selwyn and Waimakariri district councils generally require building consent for tank installation over a certain size, and for the plumbing connection into the house
• Tanks used for drinking water need to meet drinking water standards if supplying a habitable dwelling
• Backflow prevention is required where a rainwater supply is connected alongside a mains or bore supply, to stop rainwater contaminating the wider network
• Overflow needs to be managed so it doesn't cause nuisance flooding or erosion on the property or neighbouring land

Pump and pressure considerations

Unlike mains supply, a rainwater tank needs a pump to deliver usable pressure to the house. The pump is sized to the number of fixtures likely to run at once, and we usually fit a pressure vessel to smooth out the pump's cycling so taps don't surge on and off.

Combining rainwater with mains or bore supply

Many properties run a dual system, rainwater for the house with a mains or bore backup, or the reverse. This needs a properly installed backflow prevention device and a changeover or blending arrangement so the two supplies never cross-contaminate.

Ongoing maintenance

• Clean gutters and the first-flush diverter before winter and after any dusty spell
• Check tank inlet screens for leaves and debris
• Test water quality periodically if it's used for drinking
• Service the pump and pressure vessel as recommended by the manufacturer

Frequently asked questions