The term water harvesting refers to collection and storage of natural precipitation  and also other activities , aimed at harvesting surface and ground water, prevention of losses through evaporation and seepage, and all other hydrological studies and engineering interventions , aimed at conservation and efficient utilization of limited water endowment of a physiographic unit, such as a watershed . In Other words ,water Harvesting means capturing rain where it falls or capturing the run off in your own village or town. And taking measures to keep that water clean by not allowing polluting activities to take place in the catchments. The term water harvesting  is sometimes also referred to as rainwater harvesting .This is a restrictive use of the term

 In general, water harvesting is the activity of direct collection of rainwater. The rainwater collected can be stored for direct use or can be recharged into the groundwater. Rain is the first form of water that we know in the hydrological cycle, hence is a primary source of water for us. Rivers, lakes and groundwater are all secondary sources of water. In present times, we depend entirely on such secondary sources of water. In the process, it is forgotten that rain is the ultimate source that feeds all these secondary sources and remain ignorant of its value. Water harvesting means to understand the value of rain, and to make optimum use of the rainwater at the place where it falls.

Therefore, water harvesting can be undertaken through a variety of ways :  

Ø      Capturing runoff from rooftops

Ø      Capturing runoff from local catchments

Ø      Capturing seasonal floodwaters from local streams

Ø      Conserving water through watershed management  

Advantages of Roof Top Rain Water Harvesting  :  

Ø      This is an appropriate option for augmenting ground water storage in urban areas, where natural recharge has been considerably reduced due to increased urban activities and not much land is available for implementing any other artificial recharge measures. 

Ø      Monsoon run-off which otherwise flows into sewers and storm drains and is wasted is harvested and utilized. 

Ø      Rainwater is bacteriologically safe, free from organic matter and is soft in nature.

Ø      It helps in reducing the flood hazard.

Ø      It improves the quality of ground water through dilution, specially for fluoride & nitrate. 

Ø      Rain water may be harnessed at place of need and may be utilized at the time of need. 

Ø      The structures required for harvesting rain water are simple, economical and eco-friendly. 

Success Story:-

The successful example of rain water harvesting through watershed management is Sukhomajari watershed management Project. Sukhomajri, a small hamlet of about one hundred families with average land holding of 0.57 ha, is located in the foothills of Shivaliks in Panchkula district of Haryana. It is at a distance of about thirty kilometers by road to the north-east of Chandigarh. A successful experience of participatory natural resource management, which has been proved to be conducive for bringing about socio-economic and cultural transformation of the village community, has been initiated by  Central Soil & Water Conservation Research and Training Institute, Chandigarh. Until 1975, Sukhomajra had no source of regular irrigation. The entire agricultural land (52 hectares) was under rain-fed single cropping. Small land holdings (less than one hectare per family) coupled with frequent crop failures due to erratic distribution of rainfall, made agriculture least dependable as a means of adequate livelihood.

To address the problem the Research Center applied soil conservation techniques developed by comprising of mechanical and vegetative measures. This reduced the runoff sediment from the highly eroded Shivaliks at a spectacular rate from eighty tonnes to less than one tonne per hectare, within a short span of a decade. The vegetative measures consisted of planting of tree species like khair (Acacia catechu) and shisham (Dalbergia sissoo), in pits and bhabbar grass (Eulaliopsis binata) at mounds of trenches, and also Agave americana and Ipomea cornea, in critical areas to protect the soil against erosion. However, all these measures for containing the sediment in situ did not succeed in the absence of the willing cooperation from the people of Sukhomajri, who depended for their sustenance on the resources available in the catchment area. Hence, to promote agriculture and water availability in the area earthern dams were constructed. This resulted in rain water harvesting & storage which could be used by the villages for agriculture through out the year. Thus dependence of cattle grazing and rearing. The concept of social fencing gained wide recognition. The society agreed to protect the hilly watersheds from grazing and illicit cutting of vegetation and in turn, were allowed to cut grass to stall feed their cattle and collect dry and dead wood or pruned branches for their domestic fuel consumption. As a result, the forest areas which had a desolate look in the beginning of the project were covered with grass and trees within a period of 10 to 15 years. Grass production increased more than double in the same period (from 3.82 t/ha to 7.72 t/ha). 

At Sukhomajri, four earthen dams have been built between 1976 and 1985. These serve three main purposes; firstly, to check instantly the gully formation in agricultural fields and, thereby, effectively prevent silting through the erosion of soil; secondly, to store surplus rainwater from the catchment area to be used later for irrigation after the withdrawal of monsoon and thirdly, rehabilitation of the catchment.  With the availability of irrigation water mainly for rabi crops and introduction of improved agro-techniques, there was manifold increase in crop yields both for kharif and rabi.

The Departments of Forests, Agriculture and Soil Conservation, the World Bank aided Integrated Watershed Development Project (IWDP), in the North-West Shivalik States, have already implemented hundreds of such projects in this region. To site an example, till 1996 the Forest Department Haryana built approximately 93 rainwater harvesting dams covering 53 villages and about 70 such dams were built by Department of Soil Conservation, Punjab. The IWDP (Kandi Project) has adopted this model on a massive scale in the North-West Shivalik States.