Contents
Biotechnology, an exciting area within Biology Topics, applies biological knowledge to practical applications.
Three Different Forms of Water : Solid, Liquid, and Gas
Water is one of the most common and useful substances around us. Water is essential for the existence of life. All the living things (human beings, other animals, and plants) need water to live. Without water, there would be no living things on the earth. Water is available in plenty on the earth. Almost all the water on the earth is contained in the seas and oceans, rivers, lakes, ponds, snow- covered mountains, glaciers, polar ice caps, as groundwater and in the atmosphere. If we look at a picture of the earth taken from outer space, the earth appears blue (see Figure). The earth appears blue from space because a major part of the surface of earth is covered with water in seas and oceans.
It is this water on the earth which makes it appear blue. Actually, about 71 per cent of the earth’s surface is covered with water. Of the total water Figure. The earth appears present on the earth, about 97.4 per cent is in the seas and oceans.
The sea water (or ocean water) is highly salty or saline. The saline water of seas and oceans is not fit for human consumption. The water which is fit for use by human beings is called freshwater. Only 2.6 per cent of the total water on the earth is the freshwater. Most of the freshwater is in frozen state (snow or ice) on snow covered mountains, glaciers and as polar ice caps (on the poles of the earth). This frozen fresh water is not readily available for human use. Only a small fraction of freshwater is readily available for use by human beings.
In fact, the readily available freshwater for use by human beings is only 0.014 per cent of all the freshwater present on the earth. The water available for human use is mostly present in rivers, lakes, ponds, and partly as groundwater (All the groundwater is not fit for human use). Thus, a very, very small fraction of the total water present on earth is available for our use. The readily available freshwater available for use by us is only about 0.006 per cent of the total water present on the earth.
Activity
We can perform an activity to get an idea of the relative amount of water available in the various ‘sources of water’ on the earth. This can be done as follows.
(i) Take a bucket and fill 20 litres of water in it. Suppose that this 20 litre water in the bucket represents all the water present on the earth (see Figure).
(ii) Transfer 500 millilitres of water from the bucket into a mug by using a measuring cylinder. Then the water present in the mug represents the total freshwater on the earth (see Figure). The water left in the bucket represents the saline water present in seas and oceans, and unusable groundwater. This water is not fit for human use. ‘
(iii) From the mug, transfer 150 millilitres of water to a glass tumbler. The water present in glass tumbler represents the ‘usable’ groundwater (see Figure). This groundwater is fit for use by human beings. The water left in the mug represents the freshwater which is present in frozen form on snow-covered mountains, glaciers and polar ice caps. This water is not readily available for human use.
(iv) Finally, take out a quarter teaspoonful (one-fourth teaspoonful) of water from the mug. This is about 1 millilitre of water. The water in spoon represents all the water present in all the rivers, lakes and ponds of the world (see Figure).
Most of us think that water is an unlimited natural resource available to us. From the above activity we conclude that this is not so. In fact, the actual amount of water available for use by human beings, other animals and plants is very, very small as compared to the total water on the earth. Please note that even the highly salty sea water (or ocean water) can be made fit for human use but it is very, very expensive to do so. It is the water cycle taking place in nature continuously which converts some of the sea water (or ocean water) into freshwater in the form of rain and snowfall.
For millions of years, the freshwater supply on land has been maintained by the water cycle. It is due to the occurrence of water cycle in nature that even after continuous use by us, water does not get exhausted from land. We have studied the water cycle in Class VI. We can describe the water cycle in nature briefly as follows :
(i) Oceans, rivers, lakes and ponds contain water in liquid form. Evaporation of water from oceans, rivers, lakes and ponds forms water vapour which goes into air. Water vapour is the gaseous form of water. The trees and plants suck groundwater through their roots. The trees and plants put some of this water into air as water vapour by the process of transpiration (evaporation from leaves).
(ii) The water vapour present in air rises high up in the sky, gets cooled and condenses. Condensation of water vapour forms clouds. The clouds get cooled further and form rain clouds. The rain clouds make the droplets of water (formed by the condensation of water vapour) fall down on earth in the form of rain. Rain is the ultimate source of freshwater. In very cold regions, water drops in the sky freeze to form snow (ice) leading to snowfall. Snow is the solid form of water. The water which falls from clouds as rain or snow is called precipitation.
(iii) Some of the rainwater (and water formed by the melting of snow) seeps into the ground. The process of seeping of water into the ground is called infiltration. Some of the rainwater fills the lakes and ponds. And the rest of rainwater flows in the rivers and finally goes into the oceans.
Forms of Water (or States of Water)
Water exists in three forms : solid, liquid and gas. When water circulates in nature through the water cycle, it can be found in all the three forms, solid, liquid and gas, at any time somewhere on the earth. For example :
- Water is present in solid form (as snow and ice) on snow-covered mountains, glaciers and as ice caps on the poles of the earth.
- Water is present in liquid form in oceans, rivers, lakes, ponds and under the ground.
- Water is present in gas form (or gaseous form) as water vapour in the air or atmosphere around us. The continuous cycling of water in its three forms (solid, liquid and gas) in nature, keeps the total amount of water on the earth constant even when the whole world is using it.
Scarcity of Water (or Shortage of Water)
All of us need water everyday for drinking, cooking food, washing utensils, brushing teeth, bathing, washing clothes and flushing toilets. The amount of water recommended by the United Nations (UN) for drinking, washing, cooking and maintaining proper hygiene is a minimum of 50 litres per person per day. This is about two and a half buckets of water per person per day.
Only some of the people in our country get this minimum amount of water for their daily needs. Millions of people in our country do not get sufficient water. In some places there is an acute shortage of water, especially during summers. Taps running dry, long queues for collecting water, fights over sharing of water, protest marches and demonstrations for demanding more water from the civic authorities have become a common sight during the summer period (when the consumption of water increases due to hot weather).
Most of the towns and cities have water supply systems which are run by the local civic bodies. For this purpose, water is drawn from nearby rivers, lakes or tube wells. This water is purified and then supplied to all the houses through a network of pipes. Some of the villages in our country also have such water supply systems.
Many villages, however, do not have any water supply systems to supply piped water in their homes. In such villages, people fetch water directly from the source of water like river, lake or well which may be quite far off. Women and children usually walk several kilometres daily with pitchers on their heads to fetch water for their households (see Figure). This harms the women as well as the children. Women in villages have to perform a number of household chores and fetching water from far off places adds to their burden of work. The village children suffer because they spend hours in fetching water due to which they cannot attend their school regularly.
Please note that water shortage is a problem faced not only by the people living in rural areas (or village areas). Even the urban areas (city areas) face the problem of water shortage, especially during the summer season. In fact, water shortage has become a matter of concern throughout the world. It is estimated that in a few years from now, more than one-third of the people in the world could face water shortage. Though freshwater is maintained on the earth by the regular occurrence of water cycle in nature, even then there is shortage of water in many parts of the earth. Some of the causes for the shortage of water (or scarcity of water) are :
- increasing population
- growing irrigation requirements of agriculture
- rapid growth of industries, and
- mismanagement of water.
Before we go further and discuss groundwater as an important source of water, we should know the meaning of permeable rocks and impermeable rocks. A rock which allows water to pass through it is called a permeable rock. Permeable rock is a porous rock (having tiny pores in it). On the other hand, a rock which does not allow water to pass through it is called an impermeable rock. Impermeable rock is a non-porous rock. It is hard rock.