Purification of freshwater in Asia

We have considered potential sources of freshwater supply in Chapter 8 for various sub-regions in Asia. Generally we can say that groundwater tends to be less contaminated than surface water because organic matter in the water has had time to be decomposed by soil bacteria. The ground itself acts as a filtering device so that less suspended matter is present. 

H Acce to sate water, 1997 (% of Urban prrputation) O Access ro sanitation, 1997 (% of Urban populabon) 

Efforts during the IDWSSD 1980-1990 managed to increase the number of persons with access to adequate water supply in the urban areas by 46% and sanitation by 39%. However, population growth meant that the proportion of urban population served remained unchanged. In fact, the absolute number of people unserved increased by 18% for water supply and 39% for sanitation. 

The water is brought into a large holding basin to allow particulate matter to settle. Lime may be added at this stage if the pH of water is below 6.5. 

In a municipal treatment plant, aeration circumvents this problem by oxidizing any Fe + to Fe +. The rate of this reaction (1) increases with increasing pH, as follows 

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