RAINWATER HARVESTING: (reconsidering an ancient technology)

Rainwater collection in cisterns and tanks, is a traditional means of storing water for irrigation and domestic uses. It is a valuable means of reducing the impact on water sources (rivers, reservoirs and aquifiers) and the costs involved in water treatment for public consumption. There are many opportunities within households to utilise non-potable water - toilets, laundries, baths/showers, irrigation - which typically account for 60%- 90% of water consumption.

Rainwater harvesting systems typically include six components: catchment area, roof-wash system, conveyance system, cistern, delivery system, and water treatment system.

The most common contemporary catchment areas are roofs, with stainless steel or galvanized steel with a baked-on enamel, lead-free finish considered the best roofing materials for rainwater collection.

Gutters, downpipes, and piping convey rainwater from the catchment area to a filtration or storage unit. For collection systems used solely for irrigation, filtration can be as simple as leaf screens combined with a roof-wash system that drains particulates from the roof during the first flush of rain. Other appropriate filtration systems include a simple microfiltration process employing gravel, sand, and charcoal as inline filters in the collection process; To achieve potable water quality if desired, UV sterilisation; or ozonation would also be required. Cisterns can range from small drums to structures storing thousands of gallons, can be made from a variety of materials, including galvanized steel, concrete, and polyethylene. Water collection can be on a community wide scale which would provide the cheapest options to individual household collection and storage.

Such systems are low maintenance and where water catchment and secondary water use are included in the design of buildings the costs of plumbing are not high. Payback is typically 2-3 years where water usage and billing is metered.