<P> Contemporary system designs require an analysis of not only the economic and technical performance of a system, but also the environmental performance . Lifecycle assessment is a methodology used to evaluate the environmental impacts of a precut or systems, from cradle - to - grave of its lifetime . Devkota et al., developed such a methodology for rainwater harvesting, and found that the building design (e.g., dimensions) and function (e.g., educational, residential, etc .) play critical roles in the environmental performance of the system . The Economic and Environmental Analysis of Sanitations Technologies, EEAST model evaluates the greenhouse gas emissions and cost of such systems over the lifetime of a variety of building types . </P> <P> To address the functional parameters of rainwater harvesting systems, a new metric was developed - the demand to supply ratio (D / S) - identifying the ideal building design (supply) and function (demand) in regard to the environmental performance of rainwater harvesting for toilet flushing . With the idea that supply of rainwater not only saves the potable water, but also saves the stormwater entering the combined sewer network (thereby requiring treatment), the savings in environmental emissions were higher if the buildings are connected to a combined sewer network compared to separate one . </P> <P> Rainwater harvesting is possible by growing freshwater - flooded forests without losing the income from the used, submerged land . The main purpose of the rainwater harvesting is to use the locally available rainwater to meet water requirements throughout the year without the need of huge capital expenditure . This would facilitate the availability of uncontaminated water for domestic, industrial, and irrigation needs . </P> <P> Instead of using the roof for catchment, the RainSaucer, which looks like an upside - down umbrella, collects rain straight from the sky . This decreases the potential for contamination and makes potable water for developing countries a potential application . Other applications of this free - standing rainwater collection approach are sustainable gardening and small - plot farming . </P>

Why we need rain water harvesting in india