3rd Class Science Weather, Air and Water Water

       Water

Water is an essential natural resource for sustaining life. All kinds of life depend on water. Plants can prepare food only in the presence of water. Water is needed for the germination of seed. About 60 % of our body mass is comprises of water. Our blood carry lots of water, which is essential for digestion, excretion, etc. process in our body. Hence we drink lots of water every day. About % part of the earth's surface is covered with water. Ocean contains 97% of Earth's water which is salty and not suitable for drinking purposes. Water is also present in the frozen state. Fresh water or drinking water is present in rivers, lakes, ponds and underground, which is very - very less, as compared to salty water.

         Properties of Water

Look at the following picture of properties of water:

         Uses of Water

Look at the following picture of uses of water:

         Sources of Water

Ocean, lakes, rivers, ponds, seas, well, springs, rain, underground water, ice caps and glaciers at the south and north pole etc. are the sources of water. But only about 3% of Earth's water is fresh and fit for drinking. Rest are salty and not suitable for drinking purposes.

Look at the following picture of water filtration process:

         Purification of Water

Water in river, lakes etc. are contaminated with solid wastes, germs, insoluble salts, mud etc. Therefore it has to be pure or have to undergo filtration process to remove unwanted substances and to kill germs in order to make it fit for drinking purpose. Chlorine tablets and potassium etc. are added to kill germs. Now a day’s Ultraviolet rays are also used to kill germs.   

         Water Pollution

These days, due to senseless activities of human, our one of the important natural resource, water, is spoiled or made dirty; This is known as water pollution.  

         Causes of Water Pollution

Throwing dead bodies into rivers;

Pouring of dirty water into rivers from factories and industries;

Throwing of household garbage into rivers etc;

Washing of clothes and bathing of animals into rivers.  

         Problems Related to Water Pollution

On drinking contaminated water, we suffer from many diseases like diarrhoea, jaundice, intestinal problem, vomiting, nausea etc.  

         Conservation of Water

Water is a precious thing and it has to be prevented from contamination.

Every drop of water is precious. Save water, otherwise a day would come when life forms would die due to the scarcity of it. These days we are facing water crisis but we can make water available to all by following certain practices. 

Never let tap open and running when you are not doing anything.

Don't waste lots of water in cleaning, washing, bathing etc. Use only what you need.

Repair or change tap if there is a leakage.

     Which one of the following is not the characteristics of water?

(a) It boils at 100° C

(b) It is tasteless

(c) It dissolves every substances in it

(d) It is odorless

(e) It change into ice at 0°C

Answer: (c)

Explanation

Water is known as universal solvent i.e. it can dissolves many substances in it, but not all. Organic substances are not soluble in water. Therefore, option (c) is correct and rest of the options is incorrect.

     Which one of the following is the source of salty water?

(a) Ocean

(b) Pond

(c) River

(d) Seas

(e) Both (a) and (d)

Answer: (e)

Explanation

Ocean and sea are the source of salty water whereas river, pond, lake and underground water are the sources of fresh water. Therefore, option (e) is correct and rest of the options is incorrect.