hour cost watt tanks demand relief summer runoff desert systems dryland balance drought Islands dilution salinity minerals Rainwater rain fall reservoirs future use individuals urban areas water supply soil erosion domestic use storm drains coastal areas hilly terrains household needs roof catchments water available self-sufficiency flooding of roads ground water level high quality water good quality water ground water storage Harvested rain water alluvial areas energy ground water pollution pumping of ground water quality of ground water Advantages of Rain Water preferred source of water domestic water requirement fresh-saline water interface artificial recharge techniques control decline of water levels people Allegiance Water Management sub-surface ground water reservoir limited extent of fresh water aquifers Main Objective of rooftop rain water harvesting