Rainwater harvesting can (a) assure an independent water supply during water restrictions, that is though somewhat dependent on end use and maintenance, (b)usually of acceptable quality for household needs and (c) renewable at acceptable volumes despite forecast climate change (CSIRO, 2003). It produces beneficial externalities by reducing peak stormwater run off and processing costs. RH systems are simple to install and operate. Running costs are negligible, and they provide water at the point of consumption.
Rainwater harvesting can be adopted in cities to supplement the city’s other water supplies, to increase soil moisture levels for urban greenery, to raise the water table through artificial recharge, to mitigate urban flooding and to improve the quality of groundwater. In urban areas of the developed world, at a household level, non-potable uses of harvested rainwater include bathroom (i.e. shower/bath/basin), flushing toilets and washing laundry. Indeed in hard water areas it is superior to municipal water for laundry because of its compatibility with detergents and soaps. Rainwater may require treatment prior to use for drinking, depending on anthropogenic (e.g. vehicle exhaust) and natural (e.g. Coal.) contaminants.
In New Zealand, many houses away from the larger towns and cities routinely rely on rainwater collected from roofs as the only source of water for all household activities. This is almost inevitably the case for many holiday homes.
Rainwater harvesting is particularly relevant in areas such as the Garden Route where relatively good rainfall is experienced during summer and winter but due to the towns growing at a rapid rate the dams cannot cope. Water shortages have become more frequent in many towns and cities around South Africa.