Solution: 3 Marks
It's true that about $\frac{3}{4}th$ of the earth's surface is filled with water but not all of it can be used by us. The water in seas and oceans are saline water and cannot be used for day to day work. The fraction of usable water is very little and most of it is in the form of snow caps, glaciers. Only 0.006% water is available in the form of rivers, lakes, ponds, and groundwater.
Nowadays, even these sources are being contaminated due to industrial and agricultural activities. Also, due to increasing population and uneven rainfall, there is a shortage of usable water. So, we need to conserve water.