Friday, November 23, 2007

Rainwater Management and Harvesting

With the increasing frequency and severity of droughts, compounded by growing population and urbanization, the issue of water management and rainwater harvesting are receiving more attention. Projections that two thirds of the world's population will be affected by water scarcity in coming decades make the issue particularly urgent.

A paper by the Stockholm International Water Institute divides water scarcity into three categories; demand driven (use to availability), population driven (water crowding), or temporary scarcity (drought).

Demand driven scarcity can be mitigated by reducing wasteful water use—cutting leaks in supply systems, losses in irrigation, reducing excessive household use, and cleaning up pollution.

Population driven scarcity requires reallocation, raw water transfers from other basins, water desalination, the use of groundwater through pipelines, and bulk water imports.

Temporary scarcity can be mitigated by water storage, resource allocation, rainwater harvesting, and the use of terracing in irrigated agriculture.

Water shortages around the world today tend to involve a combination of these factors as population increase, industrial development and climate change combine to stress existing water systems. Paved surface areas in growing urban areas increase the amount of water that flows directing into streams, reducing the amount refreshing aquifers. Demand increases while local supplies are stressed.

The situation in the U.S. Southeast and Southwest are slightly different. The Southeast, accustomed to plentiful rainwater, now finds itself in a record drought, having to cut back on traditionally higher levels of water usage. The Southwest, with fewer water resources, began with lower water usage per capita, but population growth and a stubborn drought, also finds its water resources strained. Urbanization aggravates the problem in both areas.

Urban runoff problems can be reduced through the use of raingardens and green roofs which reduce rainwater runoff by collecting and storing stormwater so that it can infiltrate the soil. These methods also reduce the amount of pollutants that are washed into rivers and lakes.

Rainwater harvesting collects rainwater in containers of various sizes, from rain barrels attached to gutter downspouts, to much larger containers geared toward supplying landscape irrigation needs.

In the southwest, rangelands of scrub brush, grasslands, marsh areas and deserts are common environments. Here, around forty percent of all rainwater evaporates directly back into the atmosphere, while only a little over one percent recharges aquifers. Proper management of the rangelands can have a major impact on the amount of water available for human use.

Worldwide, the International Council for Local Environmental Initiatives (ICLEI), best known for its programs to help cities reduce their global warming emissions, launched a water campaign in June, 2000, to work with local governments to reduce water consumption, pollution, and systems loss. The campaign has been particularly successful in Australia, in response to the record droughts of recent years. Some localities now have extensive rainwater harvesting programs, expanding the use of collected water to toilets and other uses.

More public education is needed as water stresses continue to grow in coming years.


At 1:06 AM, Blogger barry said...

You'll find a great rain barrel design at

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At 8:22 AM, Blogger Chris Clark said...

rainwater harvesting replenishes the ground water table and enables our dug wells and bore wells to yield in a sustained manner. It helps in the availability of clean water by reducing the salinity and the presence of iron salts.

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