CBSE Class 10 Science 2017 · Paper 31/1/C · Question 24

(a) Reduce: use less of a resource, for example switch off lights and fans that are not needed, repair leaking taps and do not waste food. Recycle: collect used plastic, paper, glass and metal items and send them to be processed into new things, instead of making or extracting these materials afresh; recycling saves raw materials but itself uses some energy. Reuse: use things again as they are, for example reverse a used envelope and write on it again, or keep the bottles in which jam or pickle comes for storing things in the kitchen; this is even better than recycling because it saves the energy that recycling needs. (b) Conservation of water is necessary because (any four): (1) water is a basic necessity for all living things, needed for drinking, cooking and cleaning, by plants to make their food and by crops to grow; (2) only a very small part of Earth's water is fresh water that can be used, most of it being salty sea water or ice; (3) the demand for water keeps rising with the growing population and the needs of agriculture and industry; (4) in many places groundwater is pumped out faster than rain can replace it, so the water table keeps falling; (5) water sources are being polluted by industrial effluents and urban wastes, which reduces the usable water.