Water: a Precious Resource Class 7 Notes CBSE Science Chapter 16 (Free PDF Download)

Water

Water is an inorganic chemical substance which is the main constituent of the hydrosphere. It is tasteless, transparent, odourless, and nearly colourless substance present in almost all known living organisms. It does not provide any calories or organic nutrients but still is vital for all known forms of life.

Forms of Water:

Water generally exists in three forms on the Earth;

• Solid: In the form of ice present at the poles, at snow-covered mountains and glaciers.

• Liquid: This form of water is generally present either on the surface in the water bodies like oceans, lakes, ponds, rivers etc. or underground where it seeps below the surface through soil that gets collected over non-porous rocks (aquifer) present belowground.

• Gaseous: It includes the water vapour present in air.

Water Scarcity

The water present underground is considered as the purest form of water and most suitable for drinking purposes. Although there has been continuous depletion of the water column or the water table present belowground leading to water scarcity. The main reasons for this are as follow;

• Due to increasing population, the open areas for water seepage belowground have decreased in many areas.

• Due to the increase in the number of industries at many places, the utilization has also increased significantly for various industrial processes.

• Failure of irrigation systems due to irregular rainfall at many agricultural places lead to use of groundwater.

• The uneven distribution of rainfall at many places has also decreased the water table due to low rainfall.

• Roots of trees often help in holding the run of water but due to deforestation the water flows to lower areas instead of seeping through soil and the water table decreases.

Preventing Water Scarcity

• Sustainable water management: This can be achieved by using smart and efficient irrigation systems, water storages can be built for conservation.

• Reclaimed Water: The pressure on groundwater can be decreased by rainwater harvesting and wastewater recycling. The run of rain water can also be trapped by digging pits at different places.

• Sewage Treatments: The wastewater released from households or factories can be put into sewage treatment plants for their treatment and reuse. The sewage treatment will help in improving the water quality.

• Awareness Programs: Awareness programs should be conducted to teach people about wastage of water and how to avoid it. And how the small and necessary actions can help in water scarcity in future. 

Depletion of the Water table

Water depletion means water scarcity, which suggests that there is a lack of water.  Water collected from underground is replenished by rainwater seepage. As long as we draw the same amount of water as is replenished by natural resources such as rain, the water table does not get affected.

Reasons Behind the Depletion of Water Table

There are several reasons behind the depletion of the Water Table;

1. Over-Pumping of Water: Groundwater is the water that flows through the ground and is stored. This groundwater can be collected either by drilling or digging wells or by pumping. Over-pumping of groundwater lowers the volume of groundwater. Excessive pumping in coastal areas may cause saltwater to shift inland and upland, resulting in saltwater pollution of the water supply.

2. Deforestation: Large-scale deforestation has taken place to accommodate the increasing population in order to produce food for them and provide space for industries. Overgrazing cattle has also killed a significant amount of vegetation. The green vegetation cover slows down the flow of water to the soil and increases the absorption of water by the soil. The cutting down of trees and plants, therefore, interferes with the natural mechanisms by which the seeping takes place and the groundwater is recharged and causes depletion.

3. Increased Industrialisation: All industries use water. Somewhere in the manufacturing process, almost anything that we use requires water. The number of industries is continually growing. The bulk of the water used in the industry is drawn from groundwater. This results in water being drained.

Groundwater as an Important Source of Water

What is Groundwater?

Groundwater is water accumulated under the earth's surface. Through the surface, the water seeps and the mud soaks it. By drilling or digging a well or by pumping, groundwater is procured. Overpumping of groundwater should not be done, as it affects the soil's salinity. It lowers the level of water and increases the soil's salinity. Groundwater is also cheaper than surface water, more convenient, and less prone to contamination.

Infiltration

Infiltration is a process in which the water on the surface seeps and enters the soil. The rate of infiltration is a measure of the rate at which rainfall or irrigation can be absorbed by the soil.

Aquifer

An aquifer is an underground layer of water-bearing permeable rock, a rock fracture or unconsolidated material (gravel, sand, or silt) from which groundwater can be extracted using a water well.

Water Availability and its Forms

Earth is made up of around 71% water but only a very small part of it is freshwater. Over ninety-seven percent of the water available is salt water that cannot be used for drinking. The remaining 3% is freshwater, of which 77% of the water is frozen in the form of ice caps, glaciers, etc and the groundwater makes up 22 % of the freshwater. The remaining one percent is contained in the river, lake, pond, streams, etc., 

Forms of Water

Water is available in all three states of matter i.e. solid, liquid, and gaseous. In liquid form, water is in its normal state. Ice is the solid-state of water and the gaseous state of water is a vapour. Water is one of the few substances which is heavier in a liquid state than in a solid-state. 

Water Resources in India

In contrast to the rest of the world, India gets a lot of rainfall (rain and snow). Compared to the world's average of 700 mm, the average annual precipitation in India is 1170 mm.

Water Management

It is the task of planning, developing, distributing, and controlling the efficient use of water resources. Water supply pipes overflowing and a lot of water gushing out of the pipes is a waste of water. It is the duty of the civic authorities to avoid such wasting of precious water. Mismanagement or wastage can also take place at the level of individuals. We as an individual should also take care and should not wastewater. 

Here are Some of the Ways of Managing Water

1. Drip Irrigation: Drip irrigation is a form of irrigation that, through a network of valves, pipes, tubing, and emitters, saves water and fertilizer by slowly dripping water into the roots of different crops, either on the soil surface or directly into the root region. This saves more water than the conventional irrigation method.

2. Water Harvesting: Rainwater harvesting is the accumulation and deposition of rainwater for reuse on-site,  rather than allowing it to run off. Here, rainwater is stored for further use.

3. Cultivating Better Habits: To save water, there are numerous wise habits. We may use wise strategies to conserve water, as when washing clothes. Fixing taps that are leaky. While cleaning, hold the tap closed and take a short shower instead of a long one.