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.

(i) In the semi-arid and arid regions of Rajasthan, particularly in Bikaner, Phalods and Barmer almost all the houses traditionally had underground tanks or Tankas.
(ii) It was used for storing drinking water.
(iii) The Tankas could be as large as a big room.
(iv) The Tankas were part of the well-developed rooftop rainwater harvesting system.
(v) They were connected to the sloping of roofs of the houses through a pipe.
(vi) Rain falling on the rooftops would travel down the pipe and got stored in underground tankas.
(vii) It was extremely reliable source of drinking water especially in summer.

Four examples of hydraulic structures in India developed in ancient times are:
(i) For channelling the floodwater of Ganga, water harvesting system was built near Allahabad in the first century B.C.
(ii) Dams, lakes and irrigation systems were built during the time of Chandragupta Maurya.
(iii) Sophisticated irrigation systems were found in Orissa, Andhra Pradesh, Karnataka and Maharashtra.
(iv) In the 11^th century, Bhopal Lake, one of the largest artificial lakes of its time, was built.
(v) The tank in Hauz Khas, Delhi was constructed by Iltutmish for supplying water to Siri Fort area in the 14^th century.

Water conservation is essential mainly:
(i) To protect ourselves from health hazards.
(ii) For sustained food production.
(iii) For preservation of natural ecosystem.
(iv) For continued livelihood and other human activities.
We can conserve water by constructing hydraulic structures such as
(a) Dams
(b) Reservoirs or lakes
(c) Embankments and canals for irrigation

It is regarding the diversion of more water at Koyna by the Maharashtra Government for a multi-purpose project. This would reduce downstream flow in their states with adverse consequences for agriculture and industry.