Important topics covered in NCERT Solutions for Class 7 Science Chapter 16 Water: A Precious Resource
Water is a clear liquid that covers major parts of this planet. About 71% of the Earth's surface has water, making this planet a blue planet. Water for our daily uses comes from lakes, ponds, and rivers. "Water" is the name for the liquid state of H2O at normal temperature and pressure.
Saltwater and freshwater: Saltwater is known as seawater, which comprises a few amounts of disintegrated salts inside it. Saltwater is found in seas and oceans. Freshwater is the clean and naturally occurring water on the Earth’s surface, found in lakes and rivers, and underground as groundwater.
Statistics for availability of water
About 71% of the Earth’s surface is composed of water - 97% of the water is saltwater in seas and oceans, and the remaining 3% is fresh water in the forms of rivers and lakes. Of this 3% of fresh water, groundwater accounts for 30% while 69% is in the form of icebergs, glaciers. Now, from the remaining 1% of water, only 0.006% is used by people for their domestic use.
Types of water
Water on the surface of the Earth has been maintained for millions of years by various processes that constitute the water cycle. Water from oceans and the surface of the Earth moves into air as vapour, returns as rain, hail or snow, and, in the end, goes back to the oceans. The circulation of water in this order is known as the water cycle. This circulation of water between oceans and land is a constant process. Water that circulates through the water cycle is found in all three forms - solid, liquid, and gas. The solid forms of water found as snow and ice are present as ice caps at the poles, snow-covered mountains, and glaciers. Liquid water is present in lakes, rivers, and oceans, and even underground as groundwater. The gaseous form is the water vapour present in the air all around us.
The constant cycling of water keeps the total amount of water on the Earth sustained even when the whole planet is using it.
The water cycle is a balanced process in which water circulates and is sustained for years. Several processes that are involved in the water cycle are:
The water existing underneath the Earth's surface in rock, soil pore spaces, and cracks of the rock formations is known as groundwater. The moisture in the soil indicates the presence of groundwater. If we dig deeper and deeper, we will reach a level where all the gaps between rocks and spaces between particles of soil are permeated with water. The topmost level of this layer is called the water table. The action of percolating water from the surface of soil to the ground is called infiltration. The place where groundwater is kept in reserve in the middle of the layers of rock beneath the water table is known as an aquifer. Water in the aquifers can be normally pumped out with the help of handpumps or tube wells.
Water drawn from the ground gets replaced by seepage of rainwater. The water table does not get affected if we draw water as it is replenished by natural processes. However, the water table may go down if the water is not adequately replenished.
This may happen due to many reasons. An increase in population and industrial and agricultural activities are some common factors affecting the water table. Additionally, another factor affecting the water table could be deforestation and a decrease in the effective area for seepage of water.
Increasing population effect on the water cycle
The continuous rise in population leads to higher demand for water for domestic, agricultural, industrial, and municipal needs. Water supply is also needed for evacuation of waste materials from industries which leads to water exploitation. So, it is said the larger the population, the higher the water tension.
The varieties of water management are mentioned below:
What role can you play?
Leaking taps waste a lot of water. We must make efforts to stop these leakages. There are several ways in which you can minimise wastage of water. Few examples of how to prevent wastage of water:
Effect of water scarcity on plants
Plants require water to grow by absorbing nutrients from the soil. If plants do not get enough water, their growth and health get affected and, eventually, they die.
Water is essential for all living beings. There can be no life without it. Water exists in three forms: solid, liquid, and vapour. Though water is sustained by the water cycle, there is a severe shortage of water in many parts of the globe. There is an uneven distribution of water. A great amount of it has resulted from human activities. The rapid growth of industries, increasing population, growing irrigation requirements, and water mismanagement are some of the causes of water shortage. We need to be worried about wastage during the supply of water through pipes and through leaking taps in buildings and other places. Unnecessary use of water and overdrawing from groundwater should be avoided. Regeneration of water to the ground should be promoted. The need of the hour is that every individual uses water economically. Plants sag and ultimately dry up if not watered for a few days.
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Q1. Explain how groundwater is recharged.
Ans. The rainwater and water from different sources such as ponds and rivers seep between the soil and fill the cracks and gaps deep below the ground. The method of discharging water into the ground is called infiltration. The groundwater thus gets regenerated by this process.
Q2. Explain the factors responsible for the consumption of the water table.
Ans. Factors responsible for the consumption of the water table are as follows:
Q3. Which of the following is not accountable for water shortage?
(i) Heavy rainfall
(ii) Rapid growth of industries
(iii) Mismanagement of water resources
(iv) Increasing population
Ans. Heavy rainfall
Q4. How will you minimise the use of water to maintain a garden?
Ans. We can reduce the usage of water for gardening by adopting the drip irrigation method. By this approach, water will percolate to the roots of the plant drop by drop, which will decrease the wastage of water.