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Newsletter and Technical Publications
Rainwater Harvesting And Utilisation
An Environmentally Sound Approach for Sustainable
Urban
Water Management: An Introductory Guide for Decision-Makers
Why
Should Rainwater Harvesting and Utilisation be promoted? — The Need for
Environmentally Sound Solutions
Global
Population Growth
Global population has more than doubled since 1950 and reached six billion
in 1999. The most recent population forecasts from the United Nations indicate
that, under a medium-fertility scenario, global population is likely to peak
at about 8.9 billion in 2050.
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World population reached 6 billion in 1999.
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Given that many natural resources (such as water, soil, forests and fish stocks)
are already being exploited beyond their limits in some regions, significant effort
will be required to meet the needs of an additional three billion people in the
next 50 years.
In parallel with these changes, there have been profound demographic shifts
as people continue to migrate from rural to urban areas in search of work and
new opportunities. Since 1950, the number of people living in urban areas has
jumped from 750 million to more than 2.5 billion people. Currently, some 61 million
people are added to cities each year through rural to urban migration, natural
increase within cities, and the transformation of villages into urban areas. Urbanisation
creates new needs and aspirations, as people work, live, move and socialise in
different ways, and require different products and services. Urban environmental
impacts and demands are also different. By 2025, the total urban population is
projected to double to more than five billion, and 90 per cent of this increase
is expected to occur in developing countries.
The
Global Water Crisis
Rapid population growth, combined with industrialisation, urbanisation, agricultural
intensification and water-intensive lifestyles is resulting in a global water
crisis. About 20 per cent of the population currently lacks access to safe drinking
water, while 50 per cent lacks access to a safe sanitation system. Falling water
tables are widespread and cause serious problems, both because they lead to
water shortages and, in coastal areas, to salt intrusion. Both contamination
of drinking water and nitrate and heavy metal pollution of rivers, lakes and
reservoirs are common problems throughout the world. The world supply of freshwater
cannot be increased. More and more people are becoming dependent on limited
supplies of freshwater that are becoming more polluted. Water security, like
food security, is becoming a major national and regional priority in many areas
of the world.
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| By the year 2025, two thirds of the world population may be subject to
water scarcity. |
Advantages
of Rainwater Harvesting
Rainwater harvesting systems can provide water
at or near the point where water is needed or used. The systems can be both
owner and utility operated and managed. Rainwater collected using existing structures
(i.e., rooftops, parking lots, playgrounds, parks, ponds, flood plains, etc.),
has few negative environmental impacts compared to other technologies for water
resources development. Rainwater is relatively clean and the quality is usually
acceptable for many purposes with little or even no treatment. The physical
and chemical properties of rainwater are usually superior to sources of groundwater
that may have been subjected to contamination.
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Other Advantages of Rainwater Harvesting Include: |
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a.
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Rainwater harvesting can co-exist with and provide a
good supplement to other water sources and utility systems, thus relieving
pressure on other water sources. |
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b.
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Rainwater harvesting provides a water supply buffer
for use in times of emergency or breakdown of the public water supply
systems, particularly during natural disasters. |
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c.
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Rainwater harvesting can reduce storm drainage load
and flooding in city streets. |
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d.
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Users of rainwater are usually the owners who operate
and manage the catchment system, hence, they are more likely to exercise
water conservation because they know how much water is in storage
and they will try to prevent the storage tank from drying up. |
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e.
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Rainwater harvesting technologies are flexible and can
be built to meet almost any requirements. Construction, operation,
and maintenance are not labour intensive. |
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