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Rainwater harvesting (RwH) remained important until the introduction of mains water in the 19th century and in some dry countries it is still a vital part of their water supply (Gerolin, 2009).
Recent acceptance of problems with water shortages (United Nations Environment Programme (UNEP), 2009), flooding (Pitt, 2008) and the potential for modification of precipitation patterns, due to climate change, have reawakened interest in RwH as a means of reducing reliance on mains water and providing a certain amount of flood peak attenuation.
RwH reduces dependence on mains water that may benefit the individual householder if water use is metered, benefits the environment as less water is abstracted from lakes, rivers and groundwater, and stores excess stormwater, thus attenuating the storm peak in order to reduce flooding and, hence, reduces the pressure on the already overloaded storm sewer system (Charlesworth, 2010).
Roebuck (2007) concluded that the financial performance of RwH systems had been carried out in an ad hoc, simplistic way, by attempting to predict the cost of the harvested supply and then comparing it against an equivalent volume from the mains water supply.
However, in financial terms WLC and CBA both suggest that the smaller the installation, the increased likelihood that RwH will have a reasonable payback period, and in areas where water is metered, offer monetary savings on mains water used.
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