It’s National Water Week

2011-03-24 00:00

JULIA DENNY-DIMITRIOU looks at how a relatively small investment in equipment to harvest rainwater can have worthwhile returns for homeowners. This is another in our series on practical ways to reduce your carbon footprint and make your lifestyle more environmentally friendly


ACCORDING to a recent article in Garden and Home magazine, every millimetre of rain that falls on a square metre of roof generates a litre of water (Garden and Home, March 2011). How much water does that translate into, and how much could harvesting it save on the average family water bill? A local family is going to find out.

For some time the Edwards family of Hilton has been watering its garden with rainwater collected off the roof in a 2 500ℓ tank. “After we had a series of regular and sometimes lengthy interruptions to our municipal water supply, we decided it was time to take the next logical step and use rainwater to supplement the water supply to the house,” explained Sandy Edwards.

The family has invested in a Pedrollo pressure pump and piping installed by Graham Mallen of Will Forsyth Plumbing of Hilton. The rainwater tank is now plumbed into the house’s water supply system and supplies water for everything except drinking water, such as the washing machine, dishwasher, bath, shower and household taps. The pump switches on only when water is drawn somewhere in the house, thereby limiting the amount of electricity it uses. The rainwater tank can also be topped up with municipal water if its level falls too low.

“We keep a supply of municipal water in the fridge for drinking, but actually, the rainwater is crystal clear and often cleaner-looking than the water from the taps, especially after a water stoppage. There are control taps so we can switch between rainwater and municipal water if we want to,” Edwards explained.

It is too early to tell how much the Edwards family will save on its water bill, but according to the Garden and Home article, the way to calculate this figure is thus:

Roof area in square metres x annual rainfall in mm less 15% wastage ÷ 100 = total in kF. Subtract this amount from annual water bill = possible annual saving in rand.

A Hilton resident who keeps rainfall records recorded 1 111 mm in 2010, which translates into considerable potential savings, Mallen commented.

He said: “This is the first domestic rainwater-harvesting installation I have done, and the first of many, I hope.

“With its high rainfall, Pietermaritzburg is an ideal place to harvest rainwater for domestic use. People already use rainwater to fill their swimming pools or water their gardens, but many are waking up to its other potential uses. They are starting to realise not only the benefit to the environment of using less municipal water, but also the cost benefit. The average family can reduce its total water bill dramatically by harvesting rainwater, which is free. The investment in the equipment needed, like a pump, tank and piping, will not take too long to pay off.”

Naturally, the question every homeowner wants to ask is: “What about the cost?” Naturally, Mallen’s answer is: “That depends on the installation. The easiest way to start harvesting rainwater at home is an entry-level installation called Eco-Start Up. This is a 750ℓ storage tank fitted with a tap for filling buckets or watering cans that depends on gravity to create water flow. It can also be used to fill pools or water gardens. This costs about R3 300.”

A 2 200ℓ tank with a pump costs about R5 700. To install a system like the Edwards family has, with a 2 200ℓ tank, pump and piping into the domestic water supply system costs about R7 500.

And the next step for the Edwards family? “Solar panels,” said Sandy. “We already use gas for many things, including space heating and cooking, but to reduce our electricity consumption, the next step is obviously solar water-heating panels.”

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