The saline water from the sea gets evaporated due to the heat of sun, forms clouds and falls as rain as freshwater in the earth. A significant part of this rainwater drains out into oceans and drains. If we are able to harness this effectively, it can be an important source which can be used for various applications. So, in short, rainwater harvesting is the process of storage rainwater for reusing rather than allowing it to run off.