Class 7: Water A Precious Resource Science Chapter Notes
What causes the earth to reflect blue light, do you know?
It’s because water, which makes up 71% of the earth’s surface, reflects light in a bluish hue when viewed from a distance.
The earth’s surface is made up of 70% ocean and 30% land, respectively. Lakes and rivers occupy just under 1% of the planet’s surface. The water is salty in the oceans. For life on land, it is useless. Life on land requires freshwater. Fresh water on land is primarily obtained from rainfall. As a result, only 1% of the water in the globe is accessible for our domestic and agricultural needs.
Water Availability in Nature
Over 71% of the earth’s surface is covered with water. Consequently, our planet is also referred to as a watery planet.
Forms of Water
Water generally exists in three forms on the Earth;
Solid Form: Ice and snow on the earth are examples of the solid state of water.
Liquid Form: Water is always in a liquid state, whether it’s in the ground, rivers, lakes, or oceans.
Gas Form: Water is present in the atmosphere in the gaseous state as water vapour.
The Water Cycle
On earth, the water cycle is a constant natural process. The water cycle keeps the earth’s water supply stable. It consists of the following four phases:
Evaporation – Evaporation is the process through which water from the earth’s surface evaporates as a result of the sun’s heat. The water vapour then enters the atmosphere.
Condensation – Water vapour rises in the atmosphere, gathers there, condenses, and condenses to produce water droplets. Clouds are created when these raindrops assemble in groups.
Precipitation – Rainfall, also known as precipitation, occurs when the amount of droplets in the atmosphere increases and falls to the ground as rain. It can occasionally fall as snow in some places.
Collection – Water is stored in a variety of locations, including lakes, rivers, the sea, oceans, and underground, when it returns to the earth.
Uses of Water
Body Function: Plants prepare food using water, human and animals need for digestion and absorption of nutrients.
Domestic Use: Drinking, Cleaning, Washing, Cooking, Bathing, etc.
Agriculture Use: For farming
Industrial Use: Use to produce electricity.
Used in Transport: Ship transport goods.
Sources of Water
One of the primary sources of freshwater is rain. Rainwater that accumulates on the surface of the ground may occasionally run into nearby rivers, streams, or oceans. This water is known as runoff. In order to create a source of fresh water, the runoff water either enters rivers or is retained in lakes.
Surface water: Water collects in low-lying places after rain to create ponds and lakes. When it rains, runoff water from higher ground rushes into valleys to produce rivers in hilly areas. Additionally, seas or oceans are fed by the rivers. These various water sources combine to create the earth’s surface water.
Underground water: Water from underground sources is used by people for home and agricultural needs, particularly during the summer months or in the absence of rain.
What is Groundwater? Rainwater seeps into the gravel and rocks near the bottom, where it accumulates in the soil. The extra water seeps deeper into the earth and fills the voids between the rocks. We refer to this as groundwater.
What is Water Table?
The water table refers to the upper surface of ground water. Ground water is founds below the water table.
What is Infiltration?
Process of seeping of water into the ground.
What is Aquifer?
An aquifer is the term used to describe the rainwater that has accumulated between layers of hard rocks. The reason the water is still there is because there is a thick layer of hard rock below it that prevents the water from sinking any lower.
Depletion of water table (Scarcity of water)
The groundwater table is almost empty in several regions. This is due to the fact that it is being utilised more quickly than the natural mechanism is renewing it. The increase in use is brought about by the expansion of agriculture and the human population.
Population growth: As the population grows, there is a higher need for the development of homes, businesses, offices, industries, roadways, etc. resulting in water shortage as a result of excessive water resource utilisation.
Increase in industries: Thermal power, textiles, paper, chemicals, and metals sectors all consume significant amounts of water. Water shortages and pollution of water sources are brought on by the use of water as a cooling agent in industrial settings and for washing.
Activities related to agriculture: Farmers today bury deep tube Wells to irrigate crops, consuming significant amounts of groundwater. A region’s groundwater supply will soon become severely depleted due to the unchecked expansion of tube wells, which would cause a severe water crisis.
Water pollution: Groundwater pollution is brought on by leaking septic tanks and the contaminating effects of hazardous chemicals. Water that has been contaminated should not be consumed.
Consequences of a lack of water
On people: The lack of access to safe drinking water causes health issues and unclean circumstances.
Regarding plants: Water is essential for photosynthesis in plants. When there is not enough water, they wilt and perish.
On Land: The earth dries up on land. When water conservation techniques are not used, the area gradually turns into a wasteland.
Methods of Conservation of Water
The two primary ways to preserve water are through economical use and conservation.
Precipitation or Rainwater Harvesting: During the rainy season, a lot of rainwater pours into storm drains. By using the method of rainwater harvesting, this water can be saved for usage or to top off the groundwater levels. Rainwater from rooftops can be collected and stored in tanks to perform rainwater harvesting. There are several domestic uses for the water. The region’s subsurface water table may rise as a result of rainwater collection.
Sewage Treatments: Sewage treatment facilities can be used to treat and reuse wastewater that has been discharged from homes or factories. The sewage treatment will aid in raising the standard of the water.
Prevent dams from forming: Rainwater only seeps into the soil if it doesn’t drain away promptly. By building check dams in its course, water can be kept from draining away.
Drip irrigation: Only the area around the roots receives the necessary amount of water from the drip irrigation system. Drop by drop water delivery prevents water loss due to evaporation and runoff, hence conserving water.
Recycling industrial water and utilising it for gardening is another easy and efficient way to minimise the amount of water used.
Distribution of water in India
Rainfall in India is influenced by wind direction. Rainfall varies from location to location, and water is distributed unevenly.
Some areas, like Rajasthan, Northern Karnataka, and Gujarat, are prone to drought because of insufficient rainfall, whilst other areas, like Andhra Pradesh, Orissa, and West Bengal, get surplus rainfall that leads to floods.
Dams are constructed to distribute and preserve the water supply. The river is crossed by man-made walls that regulate the water’s flow. It has a reservoir inside of it, and the gates’ opening and closing regulates the water level in the reservoir.
What is Groundwater?
Groundwater is water that has accumulated below the surface of the ground. The water seeps through the surface and is soaked up by the mud. Groundwater can be obtained through pumping, drilling, or digging a well. It is not advisable to over pump the groundwater since it alters the salinity of the soil. It decreases the water table and raises the salinity of the land.