NCERT Solutions Class 6th Science Chapter – 14 Water Notes

Three States of Water

Water can exist in all three states – solid, liquid and gas.

Liquid state – The water that we use in everyday life is a liquid. It is called the liquid state of water.

Gaseous stat e- We have learnt that on heating, water evaporates to form its vapour. Water vapour is its gaseous state.

 Solid state – Water turns into ice on cooling. Ice is the solid form of water.

• These three states of water are Interconvertible to each other, that is, we can change it from one state to another.

Evaporation

• The process of changing water to its vapour form is known as evaporation.
• Evaporation takes place from open surfaces of water all the time-day and night.
• Evaporation of water takes place continuously from oceans, rivers, lakes, wells and soil. Oceans, seas, rivers, lakes, ponds and wells together are often known as water bodies.
• During the daytime, sunlight falls on the water in oceans, rivers, and lakes. The fields, roads, rooftops and other land areas also receive sunlight.
• The sunlight also carries heat with it. As a result, water from oceans, rivers, lakes and the soil, and other land areas gets continuously changed into vapour.
• Thus, water vapour gets continuously added to the air due to evaporation.

Transpiration

• Transpiration  It is the loss of water from the leaves of plants in the form of vapour.
• Every plant, whether it is in a crop field, a forest, on the roadside or in a kitchen garden, transpires to give off water vapour.
• The amount of water vapour that goes into air through the process of transpiration is very huge.

Uses of Water

• It is needed for drinking, bathing, washing, cleaning of vessels, toilets, flushing, etc.
• Our body contains about 70 per cent of water. Therefore, water is essential for our life.
• Water helps animals and plants to cool.
• Water is essential for the germination of seeds.
• Water is required for irrigation of the crops.
• Water is used to generate electricity.
• A water wheel is used to run flour mills.
• Water is used in many industries, like paper, rayon, petroleum refining, fertilizers, dyes, drugs and other chemical industries.
• Water is used in car radiators to keep the engine cool.
• In cold countries, people use water to warm their houses.
• Water is used to keep things cool.

Sources of Water

Rivers and springs – Most of the water that human beings use for drinking, washing and farming comes from rivers and springs. The river flows down the mountainside and across the land, finally flowing into a sea or an ocean.

Snow – Some regions of the earth are covered with snow, especially during winters. Water formed by the melting of snow is another source of water.

• This snow melts slowly. Sometimes this water flows down in the form of streams and rivers. Streams and rivers are other sources of water.

Water table – If you take soil from the ground, it has air as well as water. As you go down, the number of water increases and air decreases.

• A level below the surface, where it is only water, is called the water table.

Lakes and ponds – These are small reservoirs of water. These are created by the Collection of rainwater in low lying areas.

• Seepage from the groundwater reserves also adds to the water in lakes and ponds.

Drought – If it does not rain for a year or more at a place, the soil will lose its water by evaporation and becomes dry.

• Water will also be lost through transpiration process from the plants. Rivers, ponds and wells will dry and the water table would lower down.

• All this will affect the humans, animals and wild plants. If it continues for one or two years consecutively, it results into drought.

Consequences of drought – The result of drought may be no crops. The availability of food and fodder will decrease.

• The overall consequence of such a situation will lead to loss of life of humans and animals.

Water Conservation

•  It is very important that water should be used carefully. We should take care that water should not get wasted.

•  It is not necessary that the water used in the garden is fit for drinking. Yet most often we water the gardens with drinking water supplied by the corporation.

• We should use water for gardening that has already been used in the kitchen for washing vegetables and fruits, etc.

•  Always be careful that the water tank in your house doesn’t overflow when it is being filled.

•  Don’t use a hosepipe to wash your car or scooter. Use a bucket instead.

•  If you leave the tap running while brushing your teeth, about 16 litres of water get used up. Fill a mug with water and use it instead.

Rainwater Harvesting

• Water harvesting is the activity of collection of rainwater directly by various means.
• Harvested water can either be used immediately or it can be stored for later use.
• In Kerala and Mizoram, where it rains almost the whole year round, small tanks are used to collect rainwater, which drains from rooftops through pipes into these tanks. This water is used directly.
• In a place like Delhi where the monsoon lasts only for 3 months, it is more useful to collect rainwater as groundwater.

Water Available For Use

•  About three-fourths of the Earth’s surface is covered with water. That is why it is also called the water planet. But do you know how much water is readily available for use? Most of the water (about 97%) is in the seas and oceans as saltwater.

• This water is too salty to be used for drinking and irrigation. Thus, only a tiny fraction (about 3%) of the Earth’s water is available to us as fresh water. Out of this, 2.997% is locked up in the mountains or glaciers or is buried so deep under that it costs too much to extract.

•  So, only about 0.003% of the freshwater is easily available to us in the form of groundwater, river, lake, stream, soil moisture, and water vapour.

Uses Of Water

•  Besides being essential for life, water is used for many other purposes. In India, about 70% of the total water available is used for agriculture, 20-22% for industries and only 8% is used for personal or domestic needs.

•  Let us learn more about the various uses of water.

•  Agricultural needs Our country depends a lot on agriculture. Farmers rely on water to sustain their agricultural crops, e.g., wheat, paddy, etc.

• Many times, rainfall is not sufficient to water these crops, and farmers have to use artificial watering systems, referred to as irrigation.

•  Industrial needs Factories use a large amount of water every day—as raw material, for cleaning, heating, cooling, generating electricity (e.g., water turbines), etc. The amount required depends on the kind and size of the factory, and water.

•  Personal/domestic needs We need water to drink. Water that is suitable for drinking is called potable water. We also need water to bathe, wash clothes and dishes, clean our house, and water plants.

•  Apart from these uses, water is also used for transportation and recreation. It also regulates the climate of a place and provides homes to many animals.

The different States Of Water

•  In nature, water exists in three states. It could be in the form of liquid (e.g., rain, river, sea), solid (e.g., ice, snow, hail), or gas (e.g., water vapour).

•  You can heat water over a stove to convert it into vapour. What happens if you leave water in an uncovered vessel on a summer afternoon outside your house?

•  After a few hours, you will find that the level of water in the vessel has decreased. This is because a lot of it would have escaped into the atmosphere in the form of water vapour. The process by which a liquid is converted to its vapour is called evaporation.

•  What about the reverse process? The process by which the vapour of a substance is converted to its liquidform is called condensation. Water vapour is also added into the air by the leaves of plants, through the process of transpiration.

•  Evaporation and condensation of water take place on a very large scale on the surface of the Earth and its atmosphere. These processes play a key role in cloud formation and rain.

Cloud Formation

•  When the temperature of air increases, it expands (i.e., its particles move away from one another). This makes the air lighter and it rises in the atmosphere, taking water vapour with it. As the air rises, it begins to cool.

• The water vapour condenses on dust particles present in the atmosphere to form millions of tiny droplets. Tiny ice crystals will be formed instead if it is very cold. This cluster of tiny water droplets floating in the air is what we call a cloud.

Water Cycle

•  Water droplets in the clouds keep bumping against one another and sometimes stick to form bigger drops. When these drops become too heavy to float in the air, they drop down back to the Earth as rain.

• The water that comes down as rain, in time, evaporates and goes up to form clouds again. This leads to forming a cycle, known as the water cycle.

•  The water cycle is the cyclic movement of water from the atmosphere to the Earth and back to the atmosphere through various processes.

• Evaporation Sun’s heat changes the water in oceans, rivers, ponds, and other water bodies into water vapour. Transpiration Plants give off water vapour through their leaves.

•  Condensation Water vapour rises up and condenses on dust particles to form clouds.

•  Precipitation Water stored in clouds reaches Earth in the form of rain, snow, etc.
Collection Some rainwater seeps into the ground, forming groundwater.

•  Rainwater also flows into streams and rivers and then finds its way into seas and oceans.

Drought

•  Sometimes it does not rain for a long time – for an entire month, two months, the whole season, two years, etc.

• The abnormally long period of insufficient or no rainfall at all is called drought. During drought, rivers run dry, the water level in lakes goes down, and even the water in the soil dries up.

•  There is very little or no water available during a drought. Most plants die leading to a lack of food in the region.

• The lack of food in a region for a long period is called famine. When there are no plants, animals that survive on plants also die. Animals and humans also die due to thirst and dehydration (excessive loss of water from the body).

Flood

•  Just as too little rain is bad, too much rain is bad as well. It leads to water being everywhere, sometimes the entire area remains underwater or submerged.

• A condition when the ground becomes submerged underwater, due to heavy rain and the overflowing of rivers is called a flood.

•  During a flood, plants and crops die either due to suffocation by excess water or due to the soil being washed away, robbing their roots of support.

•  In such waterlogged conditions, many disease-causing germs start multiplying and cause water-borne diseases.

Conservation Of Water

•  Since only a small percentage of water on our planet is usable, it is very important that we use water carefully.

• Conservation of water can be done by building dams, avoiding wastage of water at homes, both indoors and outdoors, harvesting rainwater, and preventing pollution of water.

Building Dam

•  A dam is a structure built to hold back water in order to prevent floods and to provide water for irrigation and storage.

•  Building a dam is a solution to both drought and flood.

•  Dams are also used in producing electricity. Built on rivers, a dam has high walls and many openings or gates to both let in and hold backwater.

•  During heavy rainfall, when the rivers fill up, water enters the dam. When water is needed later, the gates are opened to let out water.

Rainwater Harvesting

•  The process of collecting and storing rainwater from roofs or a surface catchment is called rainwater harvesting. Storing rainwater that collects on roofs instead of letting it go down the drain, is a practical solution in case of droughts.

•  This technique is known as rooftop rainwater harvesting. This involves collecting rainwater from rooftops in dugout ponds, vessels, or underground tanks to store water for long periods.

• Another option is to allow water to go into the ground directly from the roadside drains that collect rainwater. The stored rainwater is treated before use because it may contain bird faeces, chemicals, and other pollutants, which need to be removed before use.

Preventing Water Pollution

•  Another method to conserve water is to safeguard our freshwater bodies from pollution. Garbage and harmful chemicals pollute the water and make it unfit for use. Polluted water is also very bad for aquatic life.

• Plants and animals in and around polluted water may die or get infected. And when human beings consume contaminated fish, etc., they are also put at risk of diseases.

Rainwater harvesting – The process of collecting and storing rainwater from roofs or a surface catchment is called rainwater harvesting.

•  Only a tiny fraction of the Earth’s water is available as freshwater. All living things have a lot of water in their body. Almost 70% of our body weight contains water.

•  We need water for many purposes – drinking, personal needs, agricultural needs, industrial needs, for transportation and recreation, and regulating the climate. It is home to various plants and animals.

•  Water exists in solid, liquid, and gaseous states.

•  Evaporation and condensation play an important role in cloud formation.

•  The water cycle is the cyclic movement of water from the atmosphere to the Earth and back to the atmosphere through various processes.

•  The abnormally long period of insufficient or no rainfall is known as drought.

•  When there is too much rainfall in an area, rivers overflow and water covers all the area around. This is called a flood. A flood can cause great destruction.

•  Rainwater harvesting is one of the ways to conserve water.