Water "Our Lifeline" : NCERT / CBSE Notes

We use water every day for various purposes. Water should be filtered before it is used for drinking as it contains many impurities that cannot be easily seen with the naked eye. In order to have safe drinking water, it should be boiled. 

Water "Our Lifeline", CBSE / NCERT Notes, CTET Exam Notes

Water gets contaminated by humans and it is not safe for drinking. Drinking contaminated water results in diseases such as cholera, typhoid and diarrhoea. Polluted water can also prove fatal.

Water gets contaminated and scarcity of clean water is due to the following reasons:
  • People take baths and wash clothes in rivers and lakes.
  • Many people bathe their animals in rivers and lakes.
  • Increase in the population, industries and improper disposal of waste.
Water has become so scarce that many people have to travel several kilometres to get drinking water. March 22nd is celebrated as World Water Day. It was on March 22, 2005, that the United Nations declared 2005-2015 as the International Decade for the Action “Water for Life”
Clean water is needed not only for drinking, but also for cookingwashing and bathing. A lot of waste water is produced at homes, which should be cleaned before it drains into rivers or lakes and also before it is reused.

Process of Cleaning Water

Pollutants in waste water can be removed in several stages, and this process is called “sewage treatment”. Waste water released from homes, industries, hospitals and offices, and water collected during rains from roof tops or streets, is collectively termed Sewage. This sewage is liquid waste containing dissolved impurities, and the impurities are called contaminants, which contain many harmful substances.

Sewage contains:

Organic and inorganic impurities

Organic impurities in sewage include animal waste, urine, oil, vegetable and fruit waste, faeces, pesticides and herbicides. Inorganic impurities include phosphates, nitrates and metals.

Disease-causing bacteria

There are disease-causing bacteria in sewage.

Saprotrophic bacteria

These are bacteria that feed on dead organisms.


Sewage contains some useful nutrients, such as phosphorus and nitrogen.

Other microbes

Microbes that cause typhoid, cholera, diarrhoea and dysentery are present in sewage.

Types of Sewages

There are various types of sewage, depending upon its colour and odour. Some sewage is black and has a very bad odour.

Sullage water

Waste water released from the kitchen is called sullage water. The contaminants in sullage water are mild detergents, oils and food particles. Moreover, it contains lots of water released when utensils are washed.

Foul waste

Waste water released from toilets is termed as foul waste. It consists of human waste and a lot of bacteria that release gases and bad odour. It is highly infectious.

Trade waste

Waste released from industries and commercial organisations is called trade waste. It consists of acids and strong chemicals that are toxic in nature.      


The network of small and big pipes that carry wastewater is called sewers, and all sewers together form the sewerage. Wastewater is carried from home to the point of disposal, that is, the wastewater or sewage treatment plant. After treatment of wastewater, the clean water is released into nearby water bodies. Sewerage has manholes that can be used to clear blockages. Manholes are located every 50 to 60 metres in the sewerage.
If there is no sewage facility, then waste water is directly drained into nearby streams and lakes, which results in water contamination.

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