Water for the Thousand Millions. Written by the Water Panel by Arnold Pacey (Eds.)

By Arnold Pacey (Eds.)

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Extra resources for Water for the Thousand Millions. Written by the Water Panel of the Intermediate Technology Development Group Founded by Dr. E.F. Schumacher

Sample text

If they do use more water, is this a sufficient increase to benefit health through better hygiene? , 1972) has shown that water carriers in rural areas spend a meantime of 46 min/day collecting water, though in some communities, over 4 hours per day are required. It is clear, therefore, that in regions where a substantial effort 36 ARNOLD PACEY et al is required to collect water, savings in time and energy are important benefits which water supply improvement should seek to attain—though occasionally, these are benefits in which some members of local communities (usually the men) show little interest.

Normally, the material carried by flood water is roughly 75 per cent mud with only 25 per cent sand and gravel. To ensure that only sand and gravel are deposited, the dam wall is built first to a height of only 2 m, and is subsequently heightened in stages as the sand deposit builds up. This enables flood waters to overflow the wall, 28 ARNOLD PACEY et al A sand deposited by floods B fine sand filter C coarse sand filter D slots for water intake to well E well F outlet pipe G additional sand Fig.

Apart from low rainfall and rapid run-off during storms, the water supply problems of semi-arid areas are made more acute by the high rate of evaporation experienced in the tropics, which in extreme hot climates can dispose of as much as a 3-metre depth of water in a year. The long dry season demands effective, long-term storage, but the high eva­ poration rate makes open storage reservoirs exceedingly inefficient. One technique for controlling evaporation is to use reservoirs filled with sand and loose rock.

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