NCERT Solutions For Class 10 SST Chapter 3
Question 11: Explain how water becomes a renewable resource.
Solution: Three-fourth of the earth’s surface is covered with water, but only a small proportion of it
accounts for freshwater that can be put to use. This freshwater is mainly obtained from surface run
off and ground water that is continually being renewed and recharged through the hydrological
cycle. All water moves within the hydrological cycle ensuring that water is a renewable resource.
Question 12: What is water scarcity and what are its main
causes?
Solution: Water scarcity is the shortage of water but it is not only associated with regions having low
rainfall or those that are drought-prone. 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
cases is caused by overexploitation, excessive use and unequal access to water among different
social groups.
Question 13: Compare the advantages and disadvantages of
multi-purpose river projects.
Solution: Regulating and damming of rivers affect their natural flow causing poor sediment flow and
excessive sedimentation at the bottom of the reservoir, resulting in rockier streambeds and poorer
habitats for the rivers’ aquatic life. Dams also fragment rivers making it difficult for aquatic fauna to
migrate, especially for spawning. It has great ecological consequences like salinisation of the soil.
At the same time, it has transformed the social landscape i.e. increasing the social gap between the
richer landowners and the landless poor. The dams that were constructed to control floods have
triggered floods due to sedimentation in the reservoir. Moreover, the big dams have mostly been
unsuccessful in controlling floods at the time of excessive rainfall. It was also observed that the
multi-purpose projects induced earthquakes, caused waterborne diseases and pests and pollution
resulting from excessive use of water.
Question 14: Discuss how rainwater harvesting in semi-arid
regions of Rajasthan is carried out.
Solution: 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 tanks could be as large as a big room. 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. The rainwater can be stored in the tankas till the next
rainfall making it an extremely reliable source of drinking water when all other sources are dried up,
particularly in the summers. Rainwater, or palar pani, as commonly referred to in these parts, is
considered the purest form of natural water. Many houses constructed underground rooms
adjoining the ‘tanka’ to beat the summer heat as it would keep the room cool.
Question 15: Describe how modern adaptations of traditional
rainwater harvesting methods are being carried out to conserve
and store water.
Solution: Fortunately, in many parts of rural and urban India, rooftop rainwater harvesting is being
successfully adapted to store and conserve water. In Gendathur, a remote backward village in
Mysore, Karnataka, villagers have installed, in their household’s rooftop, rainwater-harvesting
system to meet their water needs. Nearly 200 households have installed this system and the village
has earned the rare distinction of being rich in rainwater. Rainwater harvesting is once again being
conserved through modern adaptation. Rainwater running down from the roofs is not fed into
drains. Instead it is piped into underground reservoirs.
