Category : 6th Class
1. Water is a natural resource.
2. Water cycle.
3. Role of transpiration, evaporation, vaporization in water cycle.
4. Formation of hail, snow, precipitation and rains.
5. Sources of water.
6. Conservation of water.
About three fourth of Earth's surface is covered with water. Water is found inrivers, seas, oceans, soil, air, plants and animals. Man is dependent on plantsand animals which are in turn dependent on air, water and soil etc. All suchsubstances which are used by man for sustenance of life and his welfare arecalled resources and those that are found in nature are called natural resources.
Importance of water: Water is the most important substances required byus. Without water, we cannot live. Water is used in agriculture, industries, forwashing, bathing, drinking, cooking, cleaning and several other purposes. Ourbody has 70% water by weight while water melon is 99% water.
Percentage of water in food and animals
1. Several life processes like digestion, excretion, absorption of nutrientsand distribution required large quantity of water.
2. Water is the natural habitat for marine life.
3. Water is a universal solvent as it can dissolve may substances.
4. It is used in bathing, cleaning, washing, dyeing and other householdpurposes.
5. Water helps in dispersal of seeds and fruits.
6. It is used for generating steam in factories.
7. It is used in sports and recreation.
8. It is also used to generate hydroelectricity.
9. It is essential for germination of seeds and for photosynthesis.
10. Crops cannot grow without water.
11. Our body temperature is controlled by water.
12. It is also used as a mode of transportation.
STATES OF WATER
Water can exist in three states: solid, liquid and gas.
\[\to \]Ice is the solid form of water.
\[\to \]Water that we drink is the liquid state.
\[\to \]Steam is the gaseous state.
In nature, water is found in solid state as snow on high mountains. Most ofwater on earth is in liquid form found in rivers, seas, oceans and lakes. Water vapour in air is the gaseous state of water.
We can change the state of water by changing the temperature; either by heatingor cooling.
Water can be changed to ice by cooling. This is called freezing.
When ice is heated it will melt to form water. This is called melting of ice.
Similarly when water is heated, it forms steam. This is called evaporation.
Evaporation occurs at all temperature. Water from wet clothes evaporates and then clothes become dry. Wet clothes dry faster in the sun and water evaporatesfaster if the surface area is increased.
Water vapour condenses to form water on cooling. This is called condensation.
Water from water bodies like rivers, seas, oceans and lakes evaporates becauseof the heat of sun. Plants also give out water from their leaves duringtranspiration. Water vapour rises and as they reach higher up in the atmospherethey cool and condenses to form water droplets. These water droplets coalescefrom clouds. The clouds cool further and when they become too heavy, theyfall down on earth as rain. This is called precipitation.
The rainwater falls on seas, rivers and other water bodies. Water from landalso flows into rivers through streets. Some rainwater may seep undergroundas groundwater. This water is used in houses; agriculture and industries. Finallythis water too goes into rivers and seas. Snow from mountains also melt andflows into rivers. The water in oceans, seas, rivers and lakes evaporate again.
This cycle goes on and in this way water cycle goes on in nature.
Fog: During winter, sometimes, condensation of water vapours start near the surface of earth. These condensed vapour do not form rain clouds. Insteadthey appear near the earth surface as fog.
Hail or snow: Sometimes when rain falls on high mountains or when it is toocold, the water solid and becomes snow. When snow falls it is called hail.
Dew: During winter nights, when air becomes very cool, the vapours near the earth's surface condense and form water droplets. These appear as dew onleaves, flowers, railings etc.
Sources of Water
Rainwater: Rain is the main source of water. It is free from germs but maycontain dust particles. There are some dissolved gases such as carbondioxideand sometimes acids may also pollute rain water causing acid rain.
Groundwater: When rain falls on the ground, some water penetrate the soiland accumulate on the non-porous rocky layer. This is called undergroundwater and the level of water is called water table.
Sometimes the groundwater may come out at the surface to form a naturalspring. It may also form a lake.
Groundwater posses through several layers of sand and rocks. It gets filteredthrough these layers and is free from suspended impurities. However, it maybe contaminated with germs and some dissolved salts of calcium andmagnesium.
We can obtain groundwater by digging wells and tube.
About 30, 0001 of water is needed to make a card and 4500 1 to make 1 tonne of steel.
Surface water: Rainwater that runs off the surface of earth to form streams, lakes and rivers is called surface water. Snow melts and the water flows down to rivers and lakes. Surface water is highly contaminated with germs, suspendedimpurities and dissolved salts. Sewage water from houses and industries arealso discharged into rivers. River water needs to be cleaned before being
Supplied to cities and towns for drinking. Ifuncleaned water is consumed, itmay cause dangerous diseases like jaundice, cholera and typhoid.
Rivers and streams finally flow into sea and so they are the largest reservoirsof natural water. Sea water is the most impure water. It contains dissolvedcommon salt. Due to this sea water is salty and is called saline water. It is unfitfor drinking, cannot be used in irrigation and in industries.
People must use water judiciously otherwise there will be a severe water crisis.
Do You Know
Water has been the main cause of developments of some civilization like Indus valley Egyptian civilization.
Disadvantage of no rainfall at all: Rain is the main source of water. Less orno rainfall can convert an area into a desert. If there is no rainfall for a longperiod, in continuation, it may lead to drought. There will be no crop, nofood for humans and animals. There will be loss of life. An economic crisiswill occur in the region and this will become a natural calamity.
Problem due to heavy rain: If there is heavy rainfall, then also problem willrise. The fields will get flooded and crops will be damaged. Again there willbe shortage of food and fodder. Collection of rain water will also disrupt thenormal life of peoples. Many roads and bridges will get damaged and therewill be loss to life and property. Low lying areas will be flooded and peoplehave to be shifted.
Factors affecting shortage of water
(i) Increase in population has increased the demand for water.
(ii) Change in lifestyle of people has increased the consumption of water.
(iii) Urbanization has decreased the groundwater reserves as concrete roadsdo not allow seepage of water.
Industrial demand for water is increasing many times.
Conservation of water: In summers people face shortage of water becausethe level of groundwater goes down and so there is no water in wells and tubewells. If there is low rainfall the situation becomes even more grim. There isscarcity of drinking water. Therefore, management of water resources is veryimportant and in this water conservation plays an important role.
Do You Know
On an average world’s industries are four times the amount of water used by world’s entire population at home.
Measures for conservation of water
1. Development of watershed plan for drinking, irrigation and industrialareas.
2. Carrying out surveys to identify over exploited areas.
3. Artificial recharging of ground water.
4. Adoption of flood control methods.
5. Transfer of excess water to deficit areas by interlinking of rivers.
6. Adopting water harvesting methods.
7. Avoiding misuse of water.
8. Organizing people awareness programmers.
Rain water Harvesting: Rain water simply flows into drains and is lost.
Instead this rain water can be collected and used later. This is called harvestingof rain water.
Rain water from rooftops and kitchen weather can be collected in undergroundtanks. Water from these tanks percolate underground and recharge the aquifers.
Do You Know
Trees help in the process of water cycle. If deforestation occurs at the present rate, there will be insufficient rainfall. We should plant more trees.
Preventing water pollution: We can also conserve water by protecting thewater bodies from pollution. We should not dump garbage and harmfulchemicals from factor in water bodies. Dirty water is bad for marine line. Evenplants and animals die around polluted water. If humans consume pollutedwater they may suffer from many diseases.
Condensation: Process by which water vapour in air changes into liquidwater.
Evaporation: Process by which liquid water turns into vapour.
Transpiration: Process by which plants lose water in the form of water vapour into the atmosphere.
Water cycle: The cyclic movement of water from the atmosphere tothe Earth and back to the atmosphere through various processes is called water cycle.
Drought: Abnormally long period of insufficient or no rainfall is calleddrought.
Famine: Lack of food in a region for a long period is called famine.
Rain water harvesting: The process of collecting and storing rainwaterfrom roofs or a surface catchment is called rainwater harvesting.
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