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9th International Rainwater Catchment Systems Conference
"Rainwater Catchment: An Answer to the Water Scarcity of the Next Millennium."
Petrolina, Brazil - July 1999

Section 1: Strategy for Rainwater Utilization in the Next Millennium

Paper 1.1

Trends in Water Demands and the Role of Rainwater Catchment Systems in the Next Millennium

Adhityan Appan
Division of Environmental Engineering & Water Resources

School of Civil & Structural Engineering

Nanyang Technological University



The world's population has been constantly increasing and so has the water demand. However, global freshwater supplies are limited to a finite 2% of the total available water. The main aims of this presentation are to analyze global population trends, to identify the areas of major water use, to propose ways and means of reducing consumption and to appraise the potential for development of rainwater catchment systems in the next millenium.

On analysis, it is noted that demand is largely dependent on the changing requirements in the domestic, industrial and agricultural areas. Other factors that influence water demand are the ease with which it is available and its price. Population growths influence demand rates and, though populations will increase, rate of growth will decrease. Worldwide water demand has increased six fold between 1900 and 1995 though population has only doubled.

However, almost 70% of water demand is from the agricultural sector. Another phenomena that will have a great impact is the proliferation of megacities, where urban populations will predominate. By 2025, the population in these megacities is expected to double to 5 billion. That means two thirds of the world's population will be living in megacities out of which 90% will be in developing countries.

With the prospect of an escalating water demand, the search for augmenting supplies will be one of the major worries of humankind in the next millenium. The finite volumes available have to be managed optimally and it should be ensured that there is no friction between countries due to scarcity of water. Water use has to be cut down with special emphasis on agricultural practices.

With the emergence of quite a few megacities, there should be large urban populations and correspondingly rapid increases in water demand in the industrial sector. These urban populations will be sprawled over the megacities and are bound to encroach on catchment areas. As the urban poor will be quite substantial, particularly in developing countries, the catchment areas will be subjected to intense pollution. This will call for adopting effective measures to curb pollution and, as practiced in water-scare Singapore, to extensively utilize urban catchments.

With high-intensity urban populations, there are bound to be large paved and roof areas which are ideal for rainwater harvesting. Besides, medium-sized catchments areas in educational institutions, airports, army camps, etc. can be fruitfully utilized for developing individual schemes and the collected water applied for potable and non-potable uses. These smaller schemes should, preferably, be integrated with existing conventional water supply systems. The harnessing of water in megacities and the surrounding urban areas by utilizing appropriate rainwater catchment systems should alleviate, to a large extent, the future water demands.

PDF of full document (11pp, 44kb)

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