Water: A Precious Resource Question Answers: NCERT Class 7 Science

(a) True
The freshwater stored in the ground water level is much more than that present in rivers and lakes of the world as they are getting dry.

(b) False
Water shortage is the problem that is faced by all people rural as well as urban but urban areas face water problems more because the water used in urban areas are higher than the rural.

(c) False

Water from rivers are not the only source of water for irrigation process. There are various sources of water that includes dams and other man- made facilities like tube-wells etc. We can also use water from the ground (underground) for irrigation purposes.

(d) False
The ultimate sources of water are the water bodies which are present on earth including large oceans, seas, rivers, lakes etc. Rain is only the source of water returning to their original sources which they have lost by evaporation.

When the rain occurs, water oozes into the ground and then the groundwater is recharged. If, however, we keep on drawing more and more groundwater for various purposes which can be recharged by rain, then the water table will go on falling. The water table will get deeper time to time under the ground when the rain will not occurs. If this happens, then many wells, tube wells and hand pumps will dries up soon. Rain water and the water from water bodies on ground level surface pass through the soil by the process of infiltrated. This infiltrated water then get accumulated in the aquifers that is deep under the ground. There are some layers of impermeable rocks found which prevent the water in the aquifer from oozing down or leaking down further. In this way, the ground water is being recharged. 

Ten tube-wells in a lane of fifty houses can lead people to unlimited exploitation of the groundwater which can leads to depletion of the water table in the long term. If this happens then the people of the fifty houses use the ten tube wells in the need of water, then the water required by them is then drawn from the ground. If these tube-wells are also being used for long time, then the ground water level will be reduce and would go on falling. The rainwater harvesting is a method which is mainly used to conserve water at the ground level for future use or in the emergency times.

When I was told to maintain garden, I will minimize the use of water using the drip irrigation method. In drip irrigation method, water is supplied directly to the plants using narrow pipes that reduces the loss of water. Then I will check the leakages in the water pipes and arrange small pits or digs for rain water harvesting. So that the collected rain water will be used later for the various purposes. To maintain a garden’ grass or plants, water is necessary.

Steps should be taken to maintain a garden and minimise the use of water are as follows:

  1. You should not water plants through pipes because it wastes a lot of water.                                                                                                                              2. You should use drip irrigation system to conserve or save water.                                                                                                                                              3. Do not give excess amount of water to plants.                                                                                                                                                                              4. You can reuse old water and rain water or the waste water of RO that is released in the excess amount.                                                                              5. Plant flowers that need less water for the growth.

Some of the factors which affect the water table at a place and make it go falling down are as follows:

1. Increasing Population: The increasing population needs water in the higher proportion for its day full activities. As the population is increasing, more houses, shops, offices, schools, industries, roads and pavements, etc. need to be built and for this huge amount of water is required. Usually, groundwater is consumed for constructed work and this decreases the seepage of rain water from the ground. So, due to increasing population, we are consuming more groundwater and on the other hand we are allowing less rainwater to go into the ground. This leads to the depletion of water table.

2. Increasing Industries: Industries produce a large number of numerous things that we use in our everyday life. Almost everything that is made in industries needs water at some stage during the production, due to which water level is decreasing day by day. As the population is increasing, the demand for various industrial goods are increasing and hence the number of industries are also increasing simultaneously. Water used by most of the industries is drawn out from the ground which results in depletion of water table.

3. Scanty Rainfall: ‘Insufficient rainfall’ is called ‘scanty rainfall’ that means is not enough. Sometimes scanty rainfall occurs during the rainy season. Since there is less rainfall, less rainfall goes into the ground. In such a situation, much more groundwater is drawn out by the people for various purpose than gets replenished by rainfall. This leads to depletion in water table or level.

4. Deforestation: The cutting down of trees and plants from the forest for various purposes (like for the industrial area) is called deforestation. We know that forest help in bringing rain by making the air cooler and with the higher transpiration rate. So lower number of trees and plants in the forests will bring less rainfall. So, deforestation leads to lesser rainfall as well as lesser seepage of rainfall into the ground.  

5. Decreases in Effective Area for Seepage of Rainfall: Due to increasing population, urbanisation and industrialisation, more and more space is being covered by houses, other buildings, roads etc. The open spaces having unpaved ground are getting reduced on the daily basis. It is the ‘unpaved ground’ which lets the rainwater seeps into the ground and recharges the groundwater table. Since, the effective area for seepage of rainwater in urban areas is decreasing day by day, less and then less rainwater seeps into the ground which leads to the depletion of water table.

(a) Wells and tube-wells
People obtain groundwater through wells and tube-wells where water is conserved for various purposes like watering the plants etc.

(b) Ice, water and vapour
Three forms of water are Ice (when solidifies), water (when melted or taking at room temperature) and vapour (makes when water get heated).

(c) Aquifer
The water bearing layer of the earth is known as Aquifer.

(d) Infiltration
The process of water seepage into the ground is called Infiltration.

(iii) Heavy rainfall

Heavy rainfall is not responsible for water shortage unlike the rapid growth of industries increasing population, mismanaged of water resources because these all factors are responsible for the water shortage. Definitely if there is heavy rainfall, then we will never have a shortage of water and which will also results in the ground water level recharge.

(iv) Of the world remains constant

The total water in the lakes and rivers of the world remains constant or the total water under the ground remains constant or the total water in this season, oceans of the world remains constant or the total water of the world remains constant. 

                                      Groundwater and water table

Ground water is the water present beneath Earth’s surface in rock and soil pore spaces and in the fractures of rock formations. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table.