RAIN WATER HARVESTING

Harvesting of rainwater is simply the collection of water for domestic or commercial use that would otherwise go down the drain. Various techniques have been practiced for thousands of years to collect and store water, especially in areas of low rainfall. Today, rainwater harvesting systems can be installed in both new and existing buildings and can range from a quick, cheap water butt to a more complex system. Rainwater can be used for the garden, washing the car, showering, flushing the toilet, the washing machine, and even drinking if treated with UV light.
water butt: the simplest collection method is a rainwater butt connected via a diverter such as a rainsava (see below) to a downpipe from the roof - water collected can be used on the garden, using a watering can.
rain harvesting system: in a typical rainwater system water is collected from the roof and taken via pipes to a storage tank. A filter removes leaves and other debris and a settlement tank allows small particles to sink to the bottom; floating debris is skimmed off the surface via an overflow pipe, and clean water extracted from just below the surface. Water can be pumped directly from the tank to appliances or to your loft header tank. A float switch in the tank will automatically top up with mains water if the level is too low
drinking water: rainwater can be used for drinking if you install a UV sterilisation unit; the unit is switched on permanently and uses c. 40 watts. This unit will need two filters before the water reaches it – 25 and 5 microns, otherwise micro-organisms can ‘hide’ behind particles.

what are the benefits?

• rainwater collection removes the need for the energy and chemicals used to produce pure drinking water - unnecessary if all we’re going to do is clean the car with it or flush it down the toilet
• it also reduces the need for the pumping of mains water, and the energy use, pollution and CO₂ emissions that go with it
• it reduces demand on rivers and groundwater: the WWF recently reported that over-extraction by water companies is damaging Britain’s wetlands and trout rivers. The problem is most acute in the south-east, where population is increasing and millions more houses will soon be built. 86% of an average household’s water needs can be met by collecting rainwater, without further purification (33% for washing, 25% for toilet flushing, 22% for car washing and 6% for the garden)
• other benefits: rainwater is soft, and leaves no limescale; washing clothes in soft water requires less detergent and so reduces water pollution from these compounds; plants love rainwater; it doesn’t contain chlorine, which is thought to be carcinogenic; large-scale collection of rainwater can reduce run-off and therefore the risk of flooding