This process involves evaporation, condensation and precipitation.

• Disadvantages of Dams
• In recent years, multi-purpose projects and large dams have come under great scrutiny and opposition for a variety of reasons.
• The following are those reasons
• Regulating and damming of rivers affect their natural flow.
• This results in excessive sedimentation in the reservoir bed and rockier bed.
• This also results in reduced sedimentation flow in the downstream.
• These conditions are not favourable for aquatic life.
• Dams also fragment rivers. Aquatic life can’t migrate upstream for spawning.
• Dams constructed in flood plains submerges vegetation that leads to decomposition over a time.
• Multi-purpose projects and large dams have also been the cause of many new social movements like the ‘Narmada Bachao Andolan’ and the ‘Tehri Dam Andolan’ etc.
• Local people and the tribal people are always asked to sacrifice their resources, culture, tradition and livelihood for the construction of dams.
• Large farmers, industrialists and urban centres are benefitted but not the people who sacrifice for the construction of dams.
• Irrigation has also changed the cropping pattern of many regions with farmers shifting to water intensive and commercial crops.
• This has great ecological consequences like salinisation of the soil.
• It has transformed the social landscape i.e. increasing the social gap between the richer landowners and the landless poor.
• Social conflicts can also be the result of dams.
• In Gujarat, the Sabarmati-basin farmers were agitated and almost caused a riot over the higher priority given to water supply in urban areas, particularly during droughts.
• Inter-state water disputes are also becoming common regarding sharing the costs and benefits of the multi-purpose project.
• The dams that were constructed to control floods have triggered floods due to sedimentation in the reservoir.
• The multi-purpose projects can induce earthquakes, cause waterborne diseases and pests and pollution resulting from excessive use of water.

Traditional ways of Rainwater Harvesting

• In arid and semi-arid regions, agricultural fields were converted into rain fed storage structures that allowed the water to stand and moisten the soil like the ‘khadins’ in Jaisalmer and ‘Johads’ in other parts of Rajasthan.
• ‘Rooftop rain water harvesting’ was commonly practised to store drinking water, particularly in Rajasthan.
• In the semi-arid and arid regions of Rajasthan, particularly in Bikaner, Phalodi and Barmer, almost all the houses traditionally had underground tanks or tankas for storing drinking water.
• The tankas were part of the well-developed rooftop rainwater harvesting system and were built inside the main house or the courtyard.
• They were connected to the sloping roofs of the houses through a pipe.
• Rain falling on the rooftops would travel down the pipe and was stored in these underground ‘tankas’.

The first spell of rain was usually not collected as this would clean the roofs and the pipes. The rainwater from the subsequent showers was then collected