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Successful large scale application in specific regions all over the world show the relevance of roofwater harvesting. But only scarce information covering the important aspects of rainwater harvesting exist. The aim of an ongoing EU funded research is to generate reliable information for policy planners, supply professionals and ultimately householders. The research project is entitled "Domestic Roofwater Harvesting in the Humid Tropics". This zone is generally poorer than the Mediterranean and is used to low levels of water consumption. Its rainfall is generally higher and better distributed through the year. However some of the programme findings have relevance to Mediterranean needs.

Water professionals have 4 areas of concern when asked about rainwater harvesting:

water quality

economics of the system

project design to introduce, promote and spread rainwater harvesting

the information gap on what rainwater really is, its advantages and disadvantages, opportunities and potential.

It has been found that the two cheapest ways of achieving a substantial storage capacity at modest cost are to use

a simple underground 10000 litre pit lined with thin mortar and covered by a ferro-cement cone set on a low wall or

a very shallow 6000 litre cistern whose superstructure is built of informal local materials and whose lining is folded from a standard 5m x 4m rip-stop plastic tarpaulin.

 

Coliform contamination of rainwater can arise from dust particles besides human and animal sources.

The first 2 mm of rainfall is generally sufficient to wash off the contaminants, and may be separately collected as the first flush.

Water collected from a roof below a tree hanging gets heavily contaminated.

Metallic roofs possibly get hot enough to sterilise the dust particles.

Bacterial count is more at the bottom if the water is allowed to stand for some time before drawing.

Rain water was stored in plastic and cement tanks for 18 months. There was a decline in bacterial counts and no significant increase in TDS, was seen.

Using multiple sources of water is one feasible way communities have adopted to circumvent the situation of water scarcity at certain times of the year. Communities in different areas of Sri Lanka have been surveyed to find out how households use rainwater in combination with other sources to meet the entire household water requirement throughout the year. Best practices are being identified of water use in combination with rainwater harvesting.