A multi-purpose river project is a large-scale hydro project for water retention canals and irrigation, water processing and pipelines.

Objectives of Multi-purpose River Valley Projects:
1. The main objectives are:
    (a) To produce electricity from water
    (b) To improve the quality of groundwater by reducing the ground water pollution.
    (c) To conserve water
    (d) To avoid flooding of rivers.
    (e) To meet the increasing demand of water.
    (f) To augment the ground water storage and raise the water table.

(a) Post-independent India witnessed intensive industrialization and urbanization, creating vast opportunities.
(b) The ever-increasing number of industries has made matters worse by exerting pressure on existing on existing freshwater resources.
(c) Industries, being heavy users of water, also required power to run them.
(d) Moreover, multiplying urban centres with large and dense populations and urban lifestyles have not only added to water and energy requirements but have further aggravated the problem.
(e) The housing societies or colonies in the cities have their own groundwater pumping devices to meet their water needs beyond overexploited their requirements.
(f) The fragile water resources are being overexploited and have caused their depletion in several of these cities.

(a) Roof-Top Rainwater Harvesting
(i) Here, the rainwater is collected in underground tanks connected to the rooftop through pipes. 
(ii) Rain falling on rooftops travels down the pipes to the tanks and is stored for future usage.
(iii) It is also used for recharging hand pumps and tube wells.
(iv) 'Rooftop rain water harvesting' was commonly practised to store drinking water, particularly in Rajasthan.
(b) Bamboo Drip Irrigation System
(i) It was practised in Meghalaya.
(ii) It is a 200-year old system.
(iii) Here, the water from the streams is tapped using bamboo pipes and used for irrigating the roots of plants.
(iv) The long bamboo pipes are connected with each other to form a chain from the stream to the crops.
(v) The water flows through the pipes and drops directly at the site of the plant.
(c) Diversion Channels
(i) In hill and mountainous regions, people built diversion channels like the guls' or luls' of the Western Himalayas for agriculture. Diversion Channels.
(ii) In the flood plains of Bengal, people developed inundation channels to irrigate their fields.
(d) Rain fed Storage
(i) 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. 

(a) Roof-Top Rainwater Harvesting
(i) Here, the rainwater is collected in underground tanks connected to the rooftop through pipes. 
(ii) Rain falling on rooftops travels down the pipes to the tanks and is stored for future usage.
(iii) It is also used for recharging hand pumps and tube wells.
(iv) 'Rooftop rain water harvesting' was commonly practised to store drinking water, particularly in Rajasthan.
(b) Bamboo Drip Irrigation System
(i) It was practised in Meghalaya.
(ii) It is a 200-year old system.
(iii) Here, the water from the streams is tapped using bamboo pipes and used for irrigating the roots of plants.
(iv) The long bamboo pipes are connected with each other to form a chain from the stream to the crops.
(v) The water flows through the pipes and drops directly at the site of the plant.
(c) Diversion Channels
(i) In hill and mountainous regions, people built diversion channels like the guls' or luls' of the Western Himalayas for agriculture. Diversion Channels.
(ii) In the flood plains of Bengal, people developed inundation channels to irrigate their fields.
(d) Rain fed Storage
(i) 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. 

(a) It is predicted that large parts of India will join countries or regions having absolute water scarcity by 2025.
(b) Through, it is the fact that water is abundant and renewable, it is difficult to imagine that we may suffer from water scarcity.
(c) It is associated with regions having low rainfall or those that are drought prone.
(d) The availability of water resources varies over space and time, mainly due to the variations in seasonal and annual precipitation, but water scarcity in most due to the variations in seasonal and annual precipitation, but water scarcity in most cases is caused but over-exploitation, excessive use and unequal access to water among different social groups.

Rainwater harvesting in semi-arid regions of Rajasthan is carried out in the following ways
In arid and semi-arid regions of Rajasthan, agricultural fields were converted into rained Storage structures.
These allowed the rainwater to stand and moisture the soil like the Khadins in Jaisalmer and Johads in other parts of Rajasthan.
Rooftop rainwater harvesting was commonly practised or store drinking water in semi-arid and arid regions of Rajasthan, particularly in Bikaner, Phalodi, Barmer and across the towns and villages of the Thar desert.
Every house in these regions had underground tankas to store the water for drinking purposes.
These tankas are large and deep tanks which were built inside the main house. They were linked to the sloping roofs of the houses through a pipe. Rainwater falling on the rooftops would a pipe. Rainwater falling on the rooftops would run down through the pipe and collect in the underground tankas.
The collected rainwater was stored in the underground tankas providing drinking water till the next seasons. When all other sources have dried up, these tankas were beneficial to beat the summer heat as they kept the rooms cool.