Water is equally important for all forms of lives as it plays significant role in the regulation of cellular activities to activities of whole body. Water is not only important for activities that occur inside the living bodies but it is also important for economic development through uplifting agricultural and forest productivity, industrial growth ultimately supporting human well being. It is recommended by UN that people need minimum lts water/day/person for drinking, washing, cooking and sanitation. Thus, life without water can't be imagined because it is only the fuel and indicator of the life in any planet.  But we all are familiar with the fact that readily available fresh water that can be used in our daily life is very much limited equivalent or less than 1% of total water on the earth. As this limited resource has to satisfy the thrust of about 7 billion world's population, obviously a condition of water scarcity arises. Studies shows that   nearly 3 billion out of this total 7 billion people live in water scarce condition. With increase of population, global water consumption is increased by 6 times in last century, twice than the rate of population growth and it is going to increase further with the increasing new faces.

Water scarcity regarding both quantity and quality is severe problem in many region of our planet including many big cities as many cities of India, Nepal, African countries etc. It is because significant amount of rainfall is wasted as surface run off without infiltration and percolation. In many urban areas because of cementation and construction of concrete structure, artificial preservation of water, the precipitation cycle is greatly altered causing water shortage in dry season .  Although water is regarded as renewable resource, in many parts of the world water have been depleted and is very much contaminated increasing the gap between demand and availability of adequate water. Behind all these cause, global warming is still adding fuel to cause water shortage in recent decades. It is expected to give the reason by global warming of about 20% global increase of water shortage this century because it is altering precipitation pattern around the world, causing melting of mountain glaciers finally severely altering the hydrological pattern. The UN back world water commission 2000 estimates that an additional $100 billion a year is needed to tackle water scarcity worldwide.

To cope this water shortage, several new alternative technologies have been developed. Among them Rain Water Harvesting (RWH) is one of the most effective method of water collection and storage which is practiced since our ancestor's time. In our village areas generally we see collection of rain water from roof tops using bamboos in monsoon period. But it fulfills the water demand only for short period of time and is not much scientific as well. But to fight with water shortage, some advancement has been done and applied nowadays over traditional method of RWH. Today rain water is collected from roof top through drains/gutter into storage facilities as drums, surface tanks made up off metals, plastics or any type of concrete. RWH consists of capture, diversion and storage and such water can be used for different purpose as irrigation, aquifer recharge, domestic use (washing of car, toilet use etc) and so forth.

There are millions of thirsty throats whose mind dreams about easy access to water. So in water shortage areas, we should promote domestic water harvesting system which basically consists of following six basic components.

1) Catchment area It is the surface which directly receives rainfall and provides water to harvesting system.

2) Gutter and downspout It is the transportation channels from catchment areas to storage system.

3) Leaf screens and roof washer All the systems that removes contaminants and debris from collected water.

4) Storage tank (Cisterns) It includes tanks or other storage units for safe storage of collected rain water.

5) Conveying the delivery system used for treatment of rain water.

6) Water treatment It includes Settling of impurities, their filtering and finally disinfection of water.

RWH is very easy to construct with locally available materials and familiar technologies. It basically promotes sustainable water availability through economically efficient, socially acceptable and environment friendly technologies. This system is facilitated by low construction, operation and maintenance cost finally producing relatively good quality of water. It provides easy access of water at household level making household independent in water for them self eventually improving sanitation system.

The quality of rain water thus collected by RWH falls within the standard proposed by WHO. Rain water contains almost no dissolved minerals/salts and if there are any impurities found, it is removed by several treatment methods. Although few califorms are found in rain water which can be removed by solar disinfection (SODIS), chlorination and other disinfection methods.

It is found that per liter cost of such collected water is very much less than the cost of bottled water which is best at urban areas of this world to overcome water scarcity.

Increasing Water scarcity in this world is the root cause of millions of death each year due to malnourishment and water related diseases, accidents, political disputes over limited water resources etc. So as to get free from all these difficulties we must adopt RWH in potential areas.