Fresh water is a limited and precious resource that is often taken for granted. While many areas of the developing world lack supplies of safe
drinking water. Water shall be a major issue for the 21st century and water resources a real source of international and interstate conflict.

In most part of the continent, extraction of water from rivers and
underground aquifers is causing severe environmental problems. In addition rainwater run-off during rainfall from roofs and other sealed surfaces during heavy rain can lead to accumulated flooding in high-risk areas. The protection of freshwater resources must therefore be improved world-wide to ensure that drinking water does not become a luxury product.

Water is essential to all life - human, animal and vegetation. It is therefore important that adequate supplies of water be developed to sustain such life. Development of water supplies should, however, be undertaken in such a way as to preserve the hydrological balance and the biological functions of all ecosystems.

The development of water sources must be within the capacity of nature to replenish and to sustain. If this is not done, costly mistakes can occur with serious consequences. The application of innovative technologies and the improvement of indigenous ones should therefore include management of the water sources to ensure sustainability and to safeguard the sources against pollution. There is now increasing
interest in the low cost alternative-generally referred to as 'rainwater harvesting'.

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Rainwater harvesting
From Wikipedia, the free encyclopedia

Rainwater harvesting is the collection and storage of rain from roofs or a surface catchment for future productive use. This is appropriate in many parts of the world, such as western Britain, China, Brazil, Thailand, Sri Lanka, Germany and India, where there is enough rain for collection and conventional water resources either do not exist or are at risk of being over used to supply a large population. Rainwater harvesting can provide lifeline water for human consumption, reduce water bills and the need to build reservoirs which may require the use of valuable land.

Traditionally, rainwater harvesting has been practised in arid and semi-arid areas, and has provided drinking water, domestic water, water for livestock and water for small irrigation. This method may have been used extensively by the Indus Valley Civilization.

Currently in China and Brazil, rooftop rainwater harvesting is being practised for use for all the above purpose.Gansu province in China and semi arid North East Brazil have the largest rooftop rainwater harvesting projects ongoing.

Rainwater harvested from roofs can contain animal and bird faeces, mosses and lichens, windblown dust, paticulates from urban pollution, inorganic ions from the sea (Ca, Mg, Na, K, CL, S04) and dissolved gases including C02, NOx, SOx. They need to be analysed properly and used appropriately. In Gansu province for example harvested rainwater is boiled in parabolic solar cookers before being used for drinking.In Brazil alum and chlorine is added to disinfect water before consumption.Systems like SODIS (www.sodis.ch)provide low cost disinfection options for treatment of stored rainwater for drinking.

In urban areas of the developed world harvested rainwater can be used for flushing toilets and washing laundry. Indeed in hard water areas it is superior to mains water for this. It can also be used for showering or bathing. As rainwater may be contaminated, it is not suitable for drinking without treatment. However there are many examples of rainwater being used for all purposes including drinking following suitable treatment.

Two residences in the city of Toronto, Canada, use (treated) harvested rainwater for drinking water, and reuse water (i.e. treated wastewater) for all other household water applications including toilet flushing, bathing, showers, laundry, and garden irrigation (Toronto Healthy House).

In New Zealand, many houses outside of the larger towns and cities routinely rely on rainwater collected from roofs as the only source of water for all household activities. This is almost inevitably the case for the very many holiday homes that exist.

Types of Systems

There are many types of system to harvest rainwater. The type used often depends on local conditions which includes both physical and human considerations.

A mechanism can be used to send the initial water flow to waste - usually the first few liters. This method avoids most of the impurities collected on the roof, and some of the pollutants washed out of the air.

References

* Lowes, P. (1987) The Water Decade : Half Time, in Pickford (ed), 1987, Developing World Water, (p 16-17), Grosvenor Press

Case-study:
Rainwater Harvesting and Purification System - A case study is given to understand the basic process of collection and use of rainwater.
url: http://www.rwh.in/