Two third of the Earth is water. but only 3 % of it is a fresh water.rest of the water is in the oceans and seas which is too salty to be used for drinking,farming or any other purposes.

Water helps our earth from becoming too hot or too cold.2/3 of our body is also made up of water.All fruits also contains water.

Three states of matters :

We all know that water exists in three states.

Solid       Liquid       Gaseous

Water changes its form due to change in temperature.

  • Water is the only substance on earth that naturally occurs in three different forms-A solid(ice),a liquid (water),and a gas(water vapour)

Water cycle -

The water in lakes, rivers, and oceans is in liquid form.  However, every day some of this liquid turns to gas.  As the sun shines, some of the water evaporates.  Evaporation means turning from water to water vapor.

What happens to the water vapor in the air?  Some of it mixes with the air near the ground.  Some of it rises into the sky where the air is cooler.  In this cooler area, the water vapor turns back into little droplets of water.  This is called condensation.  The droplets of water form clouds.  As the water droplets get larger and heavy they fall from the clouds as rain.  Or if it is cold enough, snow.  This is called precipitation.  Rain and snow are the most common forms of precipitation.


Evaporation, condensation, and precipitation form what is called The Water CycleThe Water Cycle never stops.  It goes on and on.  It happens over and over again.

water cycle

process of water cycle -

  • Water in the ocean,seas,rivers and lakes gets heated by the sun and evaporates,forming water vapor.
  • This water vapor rises up
  • When this water vapour comes in contact with the cool air or a mountain,it condenses to form tiny drops of water.
  • The tiny drops joins together to form clouds.
  • As more join together ,the become heavy and come down in the form of rain or snow.
  • The rain water flows down into the rivers,lakes, seas and oceans.
  • Water from rivers,lakes,seas and oceans evaporates again.
  • This cycle goes on in the nature .this is called water cycle.

All living things need water to live and grow.We can live without food for sometime but can not live without water.We use water in many ways.

To Drink,to cook food,to wash utensils,to have a bath,to clean the floor,to wash clothes,to build homes,to put of fire,to grow plants

Sources of water :

Rain,rivrs,lakes and wells are the main sources of water.Water from the river flows into the sea.Dams are built on big rivers to stop water from flowing into the sea. A Dam stores water,which is used for drinking and growing crops.We get water in our homes from Dams and rivers.At some places,water is also drawn from wells.

How does water reach the taps in our homes?

River water is collected in dams and brought to our homes.

Look at the pictures.

Water pollution:

All of us need water .As our population grows,we need more water.But we need pure and clean water.Todays problems are shortage of water and water pollution.

How does water gets polluted?

Look at the picture .Observe the different ways that water gets polluted.

Water can easily become dirty or polluted and unfit for drinking.We make water dirty by throwing garbage and letting waste water flow into rivers.

Scientists are discovering that even rainwater is getting polluted.how?The fumes and smoke from factories and the exhaust fumes of moteo vehicles,goes up into the sky,mix with the clouds,and fall down witht he rain.This is called acid rain.

Water purification :

  • Boiling

Boiling water is the cheapest and safest method of water purification. Water sources and or channels of distribution may render your water unsafe. For example, parasites and germs are things you may not see by bare eyes, but their effects can be life threatening.

In this method, clean water should be brought to boil and left at rolling-boil for 1-3 minutes. For people living in high altitude areas, it is recommended to boil your water for longer than water boiled at lower altitudes. This is because water boils at lower temperatures in higher altitudes. Boiled water should be covered and left to cool before drinking. For water drawn from wells, leave it for compounds to settle before you filter out clean water for use.

  • Filtration

Filtration is one of the effective ways of purifying water and when using the right multimedia filters it’s effective in ridding water of the compounds. This method uses chemical and physical processes to purify water and make it safe for human consumption. Filtration eliminates both large compounds and small, dangerous contaminants that cause diseases with a simple and quick filtration process.. Since filtration does not deplete all the mineral salts, water that has been filtered is considered healthier compared to water purified using other methods. It’s one of the effective water purification methods that utilize chemical absorption process that effectively removes unwanted compounds from water.

Compared to reverse osmosis, filtration is considered effective when it comes to selective elimination of much smaller molecular compounds such as chlorine and pesticides. The other factor that makes filtration less costly is that it does not require a lot of energy needed in distillation and reverse osmosis. It is an economic method of water purification because little water is lost during purification.

  • Distillation

Distillation is a water purification method that utilizes heat to collect pure water in the form of vapor. This method is effective by the scientific fact that water has a lower boiling point than other contaminants and disease-causing elements found in water.

Water is subjected to a heat source until it attains its boiling point. It is then left at the boiling point until it vaporizes. This vapor is directed into a condenser to cool. Upon cooling, vapor is reversed into liquid water that is clean and safe for drinking. Other substances that have a higher boiling point are left as sediments in the container.

This method is effective in removing bacteria, germs, salts and other heavy metals such as lead, mercury and arsenic. Distillation is ideal for people who have access to raw, untreated water.

This method has both advantages and disadvantages.

A notable disadvantage is that it is a slow process of water purification.

In addition, it requires a heat source for the purification to work. Although cheap sources of energy are being developed, distillation remains a costly process of purifying water. It is only ideal (effective and least costly) when purifying small quantities of water (It is not ideal for large scale, commercial or industrial purification).

  • Chlorination

Chlorine is a powerful chemical that has been in use for many years to treat water for home consumption. Chlorine is an effective water purification method that kills germs, parasites and other disease-causing organisms found in ground or tap water. Water can be purified using chlorine tablets or liquid chlorine. As an off-the-shelf water purification product, chlorine is cheap and effective. However, caution should be taken when using chlorine liquid or tablets to treat drinking water.

For example, people suffering from thyroid problems should talk to a medical practitioner before using this product. When using chlorine tablets, it is important to apply them in heated water, as they dissolve well in water that is at 21 degree Celsius or higher. Chlorine tablets kill all bacteria leaving your water clean and safe.

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