Rainwater harvesting for domestic use and as drinking water source is becoming increasingly popular and necessary as the availability of good quality water declines. Rainwater is acknowledged as a sustainable source of water that has less impact on the environment. Households and communities have augmented or substituted their household supplies with rainwater for reasons of scarcity, salinity, quality of service and for risk substitution. While rainwater may not always provide a full-year round of supply, it enhances water security in the house and generally provides a good quality water. Rainwater may be the sole source of water in countries like the Maldives and upland Sri Lanka, provide an alternative to arsenic-laden ground water in Bangladesh and augment inadequate urban supplies from Chennai to Kathmandu and scattered households in the mountain ridges in Bhutan. Its use is nowadays promoted by Governments and NGOs alike for numerous domestic applications like drinking, cooking, bathing, laundry, toilet flushing and for gardening purposes. Infiltration to sustain local aquifers is suggested as well.
Rainwater harvesting basically means capturing rainwater from the roofs of buildings on the residential areas, courtyards, playgrounds, hill slopes, places of worship, institutions etc.However, rainwater can also be harvested by those who do not have a proper roof by creating temporary collection surface by using a clean cloth piece. A rainwater harvesting system consists of; catchment area (Roof), conveyance system (guttering, downspouts and piping), filtration (screen), storage (cistern), disinfection (filtration, chlorination) and distribution system. Water harvesting can be done at the household level or in a community, schools, offices etc.
Harvested rainwater could be stored for ready use in tanks (above or below ground) or charged into the soil and thus could control declining water table (Groundwater recharging). Additionally, storage of significant quantities of safe water at the household level is a suitable preparation for disasters that interrupt water supplies. Therefore, roofwater harvesting has a possible role both in emergency responsiveness and in disaster relief. It is a significant source for water for an individual, family or a community. Rainwater harvesting is widely practiced in Maldives, India, Sri Lanka (it especially benefited the Tsunami hit populations), Myanmar (more so, after the cyclone Nargis), Bhutan, Bangladesh (as an alternate drinking water source for arsenic affected areas) and Thailand.