Water is one of the essential element for life on earth. Most of the earth’s surface is covered with water. Any guesses on how much fraction of the earth is covered with water?
About three-fourth of earth’s surface is covered with water.
An interesting fact for you to know is that most part of the human body consists of water.
We need water in daily life for different purposes: drinking, washing clothes and utensils, cooking, watering plants to name a few. As already stated most of the earth’s surface contains water, yet all of it can not be utilised. So how and from where do we get water for daily use?
In this chapter, you will learn about sources of water, different states of water, water cycle, the importance of water, water-borne diseases, and finally purification of water.
Sources of water
- Most of the earth’s surface is covered by the oceans.
- Sea is the largest source of natural water, but it contains a high amount of dissolved salt and cannot be used directly for irrigation or drinking.
- Rivers and lakes contain water that comes from glaciers or rainfall. As rivers flow downhill and through plains, they collect many substances like minerals, organic matter, clay. Sometimes bacteria may also be present in river water.
- We meet all our domestic and industrial requirements of water from rivers.
- Ground water is a pure form of water because it has no suspended impurities or germs. However, it may have dissolved minerals which give it a distinct taste and even medicinal properties.
- We can obtain ground water by digging wells.
- Rainwater is the purest form of water.
- It will contain dissolved substances like dust, carbon dioxide, oxygen and nitrogen.
States of water
- Water exists in all three states of matter: solid, liquid and gas.
- Ice, water and steam have different physical properties but same chemical properties.
- The interconversion of these three states of water also occurs in nature and it is called the water cycle.
Water cycle
Evaporation:
Heat from the Sun causes water on Earth (in oceans, lakes etc.) to evaporate (turn from the liquid into the gas) and rise into the sky. This water vapour collects in the sky in the form of clouds.
Condensation:
As water vapour in the clouds cools down it becomes water again, this process is called condensation.
Precipitation:
Water falls from the sky in the form of rain, snow, hail, or sleet, this process is called precipitation.
Collection:
Oceans and lakes collect water that has fallen. Water evaporates into the sky again and the cycle continues.
Importance of water
Commercial water use includes fresh water for motels, hotels, restaurants, office buildings, other commercial facilities, and civilian and military institutions. Domestic water use is probably the most important daily use of water for most people.
Domestic use includes water that is used in the home every day, including water for normal household purposes, such as drinking, food preparation, bathing, washing clothes and dishes, flushing toilets, and watering lawns and gardens.
Industrial water use is a valuable resource to the nation's industries for such purposes as processing, cleaning, transportation, dilution, and cooling in manufacturing facilities. Major water-using industries include steel, chemical, paper, and petroleum refining. Industries often reuse the same water over and over for more than one purpose.
Irrigation water use is water artificially applied to farm, orchard, pasture, and horticultural crops, as well as water used to irrigate pastures, for frost and freeze protection, chemical application, crop cooling, harvesting, and for the leaching of salts from the crop root zone.
Nonagricultural activities include self-supplied water to irrigate public and private golf courses, parks.
Potable water:
Potable water is required for human consumption (drinking). It must be:
- Clean and transparent.
- Free of germs and suspended impurities.
- It should contain some amount of gases and minerals so that it does not taste flat.
- It should not have harmful chemicals.
Waterborne diseases
Drinking dirty or contaminated water causes water borne diseases.
Some waterborne diseases are:
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Purification of water
Water must be treated or purified to make it fit for human consumption.
Coagulation stage:
- Alum and other chemicals are added to the water at this stage.
- Suspended particles get stuck to the chemicals to form 'floc'.
Sedimentation Stage:
- As particles get stuck they become heavy and sink to the bottom of the chamber.
- At this stage, most of the particles are stuck to form sediments, sinking to the bottom.
- The water is passed onto the Filtration chamber.
Filtration stage:
- As water passes slowly through this chamber, finer particles (sediments) are filtered out over layers of sand, charcoal and gravel.
Disinfection stage:
- Chlorination or addition of chlorine to water is used to kill any bacteria and other living organisms that may be in the water.
- It is very normal and natural for fresh water to contain living organisms.
Ozonization:
- Because of its excellent disinfection and oxidation qualities, ozone is widely used for drinking water treatment.
- Ozone can be added at several points throughout the treatment system,
Storage stage:
- The water is then passed into large storage tanks and left for a while for the action of disinfection to be complete.
- At the tail end of this storage tanks, huge pipes are connected to transport water to our homes and workplaces.
- At home, the easiest way to sterilise water is by boiling. Boiling water kills germs and makes it safe for drinking.
- Filtering through a cloth also removes soil and other large particles.
- Chlorine can be added to overhead tanks to disinfect water.
- Apart from this, we can also install RO systems or water purifiers with activated carbon filters to purify water.
Any liquid in which a solid dissolves easily is known as a solvent. Water has this excellent property of dissolving many substances.
Can you name one or two substances which you use every day, which easily dissolves in water?
They are the salt and the sugar.
Similarly, there are many other substances which dissolve in water. Hence, the name universal solvent for the water. In this chapter, you will learn more about water as a solvent and you will also learn step-by-step procedure to prove that tap water and sea water contain dissolved solids and gases.
- Water has the ability to dissolve many substances in it. However, water dissolves different amounts of different substances under the same conditions. For e.g., for the same volume of water, we can dissolve more sugar than salt.
- Aquatic life depends on the oxygen dissolved in water.
- Stirring and heating increase solubility of a substance.
- Pure water is transparent, colourless, tasteless and odourless.
Temperature and solubility:
- Add a 1/2 cup of lukewarm tap water to a plastic cup.
- Weigh about 5 tablespoons of salt and gradually add the salt to the tap water, stirring to mix.
- Stop adding salt when it no longer dissolves.
- Repeat the mixing steps with 1/2 cup each of ice water and hot water; determine at which temperature more salt dissolves.
- This experiment proves that the solubility of some substances is dependent on temperature, and we observe that much more salt dissolves in hot water than in cold.
Experiment to show that tap water and sea water contain dissolved solids and gases
- Two round bottom flasks are filled with tap water and sea water respectively and heated. Bubbles of gas will be released from the water and travel into the test-tube. Continue until the contents of the flask are boiling.
- About half a test-tube full of gas will be collected in each case, all of which has been displaced from solution by heating.
- A glowing splint continues to glow and does not immediately go out when placed in the gas.
If both samples of water are placed in an evaporating dish and allowed to evaporate, the water completely evaporates leaving behind traces of solids in the dish, showing that the samples of water contain dissolved solids.
Water plays a very important role for all of us in daily lives. You might postpone eating food, but you definitely need water to quench your thirst. Even though most of the earth’s surface is covered with water, most of it is unusable.
Have you tasted sea water?
In case you have, it is very salty, right?
So, one of the main sources of water is rain. Rainwater is collected in rivers, tanks, reservoirs which are available for use by all living beings. It is essential to conserve water and make sure that the water is not polluted by industrial waste or any such means, water is not wasted and so on. It is the responsibility of all of us to preserve and conserve water for generations to come. In this chapter, you will learn about the importance of water, water conservation, water pollution and preventing water pollution.
- Water is a precious natural resource and we must conserve water.
- We can conserve water by using it in a wise manner.
- 97% of all the water on the earth is salt water, which is not suitable for drinking. Only 3% of all the water is fresh water, and only 1% is available for drinking. That is why we must conserve water.
A few simple ways to reduce usage and wastage of water:
- Turn off the tap when you brush your teeth.
- Fix a dripping tap and leaking pipes.
- Use a bucket instead of the shower.
- Water your garden with a watering can rather than a hosepipe.
- Rainwater harvesting is used by many people to save and use rainwater.
- Use drip irrigation on fields.
- Grow more trees to maintain water cycle.
- Avoid water pollution.
- Build dams to store and conserve water.
Water pollution:
- Sewage, kitchen and industrial wastes are dumped into the water.
- Chemicals from farms (dissolved fertilisers) and acidic waters from mines and industries pollute the water.
- Nuclear and thermal power plants use water for cooling purposes and discharge the hot water into seas and rivers. This causes an increase in temperature of the water and kills fish and plants in the water.
Water pollution can be controlled by:
- Treatment of sewage before being released into rivers.
- Removal of solid waste and garbage from sewage.
- Avoid using detergents, fertilisers, plastics and pesticides which can increase the chemical content of the water.
- Treat all effluents from factories to make them harmless.
- Avoid using lakes, ponds and rivers for bathing, washing animals and defecating and for disposing of dead bodies.
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