Day by day groundwater depletion is increasing and contamination of surface water which is generating vigorous threat to our future. Rainwater Harvesting could be one of the most sustainable sources for addressing this issue.

Rainwater harvesting is widely used term covering all those techniques whereby rain is intercepted and used 'close' to where it first reaches the earth. The typical use of this intercepted rainwater are drinking and domestic use (after proper treatment), garden irrigation, water closet flushing, etc. Often the rainwater is just redirected to deep pit for percolation (artificial groundwater recharge). Rainwater harvesting is an old technology; it has been practiced in the different cultures and societies in different parts of the world from ancient times. Yet, a renewed interest regarding this technology among modern-day engineers and water practitioners has been observed mainly due to few reasons: 

- RWH can be considered as a probable solution of drinking water crisis in areas where there are no possibilities of providing safe water cheaply within a reasonable distance of homes because the groundwater conditions are unsuitable and surface water is polluted or absent. 

- In the context of the urban environment, adopting rainwater harvesting technology can reduce the pressure on municipal water supply. 

There are few advantages and disadvantages also; here I mention a few of them: 

Advantages:

- Rainwater is sodium free, which is important for persons on low sodium diets. Though it comes to earth directly so there are no possibilities to get any bacteria or viruses. 

- It helps on groundwater pressure and also recharges.

Disadvantages: 

- Initially establishing RWH system is high.

- Maintainance is also one of the disadvantages. 

In urban areas, most buildings have a water demand for the purpose of the building. Activities or facilities in a building requiring water include water include bathrooms, kitchens, manufacturing process, fire suppression, cooling towers and so forth. The necessary task is to determine what percentage of that building's demand can be met by site collected water. For practical reasons and to meet limited budget requirements, replacing all of a building's water consumption with roof-collected rainwater is not necessarily the end goal. Alternatively, the design goal is to provide as much of the necessary water supply from rainwater or alternative water sources, thus reducing the demand on the municipal water system.