Turbocharging your water harvesting
Harvesting water at home can be a hassle unless you have a smart system.
In areas with reticulated water supplies, most rainwater-capture systems are simple tanks attached to guttering downpipes. Sadly, there is not enough water pressure to make it really useful. You can fill a watering can from it but it won’t drive a sprinkler system, and unless you have a decent fall on your garden that water is likely to be under-utilized.
If you are keen enough to install a large tank and pump you can get decent pressure in your hose and you can divert tank water to the laundry and toilets as well as garden taps. But now it gets serious, as you have to plumb in supplies to those parts of the house, and you have to be able to switch between tank and reticulated supply when the tank runs low. Just thinking about switching back and forth manually — let alone remembering to think about doing it manually — is exhausting.
That’s why Garth Cohen at
White International, which supplies all manner of water supply systems, is such a fan of automatic changeover devices. These devices, which control the tank’s water pump, ensure that tank water is used first to get maximum benefit from it, then when the tank runs low, they seamlessly switch in the mains supply. Twenty-four hours later the dedicated pump controller will check the tank level again, and if it has captured enough rainwater it will start drawing from the tank again and the changeover device then will switch back to using tank water. Your tank water doesn’t get the chance to sit around doing nothing.
Garth says that these systems are top sellers in Australia where councils have brought in rules that insist on harvesting. They still make perfect sense in new builds here, but in rainy New Zealand, most council and health authorities are more focused on making sure untreated water doesn’t get into the pipes supplying potable (drinking) water. They require backflow prevention devices (RPZs) installed in systems where changeover devices switch between tank and mains supply. And the non-potable supply lines have to have different-coloured piping and signage.
This may appear baffling to people in rural areas who literally live off tank water but they are more likely to have UV or other treatment systems. Some may have conditioned their immune systems to local conditions but health authorities also suspect people on untreated supplies simply have more unexplained illnesses. And as for using grey water from sinks and showers for garden watering or flushing toilets — both common overseas — councils and public-health officials won’t even set standards, which, by government logic, makes it illegal.
Submersible pump for in-tank installation