NCERT Solutions For Class 7 Science Chapter 18

NCERT Solutions For Class 7 Science Chapter 18 PDF Free Download

The NCERT solutions class 7 Science chapter 18 – Wastewater Story is crucial for the students of 7th standard. The solutions are provided here to assist the students in understanding the Wastewater Story in an easy and interesting way.

NCERT Solutions for Science Chapter 18 – Wastewater Story are prepared and compiled by subject experts as per the latest CBSE syllabus (2018-2019). It is important for the students to practice the solutions regularly for effective preparation of the examination.

Introduction to NCERT Solutions Class 7 Science 8 Wastewater Story

This chapter specifically deals with the issue of contaminants in the water. Water is an important resource not just for humans but for all the organisms on earth. Therefore, contaminating this natural resource has dire consequences. The main reasons for water pollution are our commercial and industrial activities. All the waste effluents that reach water bodies results in water pollution. In the long run, this can cause many diseases and health hazards for us.

As a reference to 7th class students, we are offering wastewater story class 7 notes, wastewater story class 7 extra questions with answers in PDF, they can download them and read whenever they required. 

For instance, in Minamata City, Japan, mercury which runoff from a factory polluted the waters and the poisoning went undetected for decades. It came to notice only when the people saw their new-borns had unusual birth defects. It was found that mercury runoff had contaminated the marine ecosystem, primarily fish species ingesting the mercury. Over a period of time mercury accumulation in fish species got transferred into human bodies who consumed contaminated fishes. This adversely affected bodily functions and caused a lot of problems for the people and their descendants. Hence, we need to take care of such issues by preventing industrial effluents polluting our most precious resource – water.

Topics Covered in 7th Class Science Chapter 18 Wastewater Story:

Wastewater Story Chapter has 8 subtopics which are listed below.

  1. Water our lifeline
  2. What is sewage
  3. Water freshens up-an eventful journey
  4. Wastewater treatment plant
  5. Better housekeeping practices
  6. Sanitation and diseases
  7. An alternative arrangement for sewage disposal
  8. Sanitation at public places

Find out more about wastewater below.

Q1. Fill in the blanks:

  1. Cleaning of water is a process of removing _______.
  2. Wastewater released by houses is called _______.
  3. Dried _______ is used as manure.
  4. Drains get blocked by _______ and _______.


  1. Pollutants
  2. Sewage
  3. Sludge
  4. Chemicals, Kitchen waste


Q2.What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.

Ans. Water containing liquid wastes disposed from domestic household activities, industrial activities and agricultural activities is termed as sewage.

The untreated sewage can harm the rivers and seas as the contaminated water pollutes the whole source of water. As the sewage water may contain harmful substances and disease causing organisms, it is dangerous to release the untreated sewage into the water bodies.


Q3. Why should oils and fats be not released in the drain? Explain.

Ans. Water flow is affected by the blockages produced due to the release of these oils and fats into the streams of water flowing in the drain.They harden the soil in the pipes and results in a block. The holes of the soil in the drains gets clogged by the Fats. Hence, the flow is affected.


Q4. Describe the steps involved in getting clear water from wastewater.


  1. These are the steps involved in the purification of water,
  2. In the first step, all the physical impurities like stones, plastic bags ,cans etc. are removed by passing the water through screens.
  3. Now, water is subjected to sedimentation where impurities are removed by the force of gravity.
  4. Solids settled at the bottom of the sedimentation tank is removed. This is called sludge.
  5. An aerator cleanses the water from other impurities.
  6. Chlorination is done to remove all disease causing bacteria.


Q5. What is Sludge? Explain how it is treated.

Ans. The solid waste collected along with the wastewater during the treatment in the treatment plant is called sludge. It is decomposed in a separate tank by the anaerobic bacteria. The product is called Activated sludge process in which the activated sludge can be used as manure.


Q6. Untreated human excreta is a health hazard. Explain.

Ans. A lot of health hazard may be resulted from untreated human excreta. Besides polluting air, water and soil it could also cause epidemics like Cholera, Meningitis etc,. when it mixes with water.


Q7. Name two chemicals to disinfect water.


  • Chlorine
  • Ozone


Q8. Explain the junction of bar screens in a wastewater treatment plant.

Ans. Physical impurities with considerable size can be removed by Bar screens. The screens are made of meshes which permit water and finer solids to pass through while restricting bigger solids.

Eg:Plastics, Wood chunks, Papers, cans, Food wastes.


Q9 .Explain the relationship between sanitation and disease.

Ans. Proper sanitation should be maintained in order to avoid diseases. They are related to each other. By sanitation, proper disposal of sewage and refuse from household and public places is carried out. Implementation of proper sanitation results in a state where we are free from any diseases. Lack of it may lead to various diseases.


Q10. Outline your role as an active citizen in relation to sanitation.


  • We should take care of our personal sanitation
  • Efforts should be taken to make people aware of the benefits of sanitation.
  • With the help of municipal corporations, all the open drains should be covered.
  • We should remove all the disease causing substances thrown in open.


Q11. Solve this crossword puzzle.




  1. Liquid waste products
  2. Solid waste extracted in sewage treatment
  3. A word related to hygiene
  4. Waste matter discharged from human body


  1. Used water
  2. A pipe carrying sewage
  3. Micro-organisms which cause Cholera
  4. A chemical to disinfect water




12.Study the following statements about ozone:


  1. It is essential for breathing of living organisms.
  2. It is used to disinfect water.
  3. It absorbs ultraviolet rays.
  4. Its proportion in the air is about 3%.


Which of these statement are correct?

I. (1), (2) and (3)

II. (2) and (3)

III. (1) and (4)

IV. All four

Ans. (II) (2) and (3)

Water is a resource that we use for almost all of our activities. And consequently, polluting this resource can adversely affect our health. It is mainly polluted by human activities as a result of commercial or industrial exploits. The waste by products contain many poisonous chemicals that disrupt the marine ecosystem. Also, human excreta poses a major threat and could potentially be a bio-hazard due to many harmful microbes it carries. These microbes or chemicals could leech into the aquatic environment tainiting every life form that comes in contact with it.

NCERT Solutions Class 7 Wastewater Story guides the students to segregate waste in a way to reduce water pollution. This chapter demonstrates the importance of water in balancing the ecosystem. Students will get to study the meaning of sewage, its treatment and disposal methods. This chapter creates an awareness of sanitation in students which help them to become responsible citizens.

Check here to refer the other NCERT Solution for Class 7 Science Chapters.

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