Rain water harvesting is a process in which rain water is collected directly in reservoirs.this water is used for domestic and agricultural purposes.the harvesting methodto be adopted depends on the frequency and quantity of rainfall.the simplest rain water harvesting method is to collect rain water from roof tops of buildings storage water reservoirs through conduit the rooftop is the attachment area the amount and quality of collected water will depend on the ground material.rain water harvesting has become a very popular method of conserving water.the advantages of this method is it requires little maintainance cost and it is environment friendly.