NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story

Edited By Shivani Poonia | Updated on Apr 09, 2025 09:48 AM IST

Water is essential for all life forms and is basic to our survival. So, it is highly important to use water wisely and avoid wasting it. Chapter 13 of the Class 7 Science textbook, titled “Wastewater Story,” will help students understand how water gets polluted and how it can be cleaned before being released back into nature. The chapter answers important questions like- What is sewage? How is dirty water treated to make it safe again? It also introduces important concepts like aeration, sewage treatment, aerobic and anaerobic bacteria, biogas, and how wastewater can be recycled and reused.

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Download PDF of NCERT Solutions for Class 7 Science Chapter 13 Wastewater Story
NCERT Solutions for Class 7 Science Chapter 13 Wastewater Story Exercise:
Wastewater Story Class 7 Science Chapter 13-Topics
Chapter-wise NCERT Solutions of Class 7 Science
Benefits of NCERT Solutions for Class 7 Science Chapter 13 Wastewater Story:

The NCERT Solutions fo r Class 7 Science Chapter 13 provide clear and detailed answers to all exercise questions available in the textbook. These solutions not only help you understand the root cause of the water pollution but also tell you the ways to preserve it.

In addition to this chapter, NCERT Solutions from Class 6 to 12 are a great resource for students who are studying under the CBSE syllabus. They help you understand tricky science topics with simple explanations and examples. Scroll down to go through the questions and answers given in the article below.

Download PDF of NCERT Solutions for Class 7 Science Chapter 13 Wastewater Story

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NCERT Solutions for Class 7 Science Chapter 13 Wastewater Story Exercise:

1. Fill in the blanks:
(a) Cleaning of water is a process of removing ____________.
(b) Wastewater released by houses is called ____________.
(c) Dried ____________ is used as manure.
(d) Drains get blocked by ____________ and ____________.

Answer:

(a) Cleaning of water is a process of removing contaminants.
(b) Wastewater released by houses is called sewage.
(c) Dried cow dung is used as manure.
(d) Drains get blocked by plastic and fats.

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

Answer:

Sewage is wastewater coming out of households, public places, farms, and industry. It also includes rainwater that has flown into the sewers.

Untreated sewage contains harmful chemicals, which, if released directly into the rivers or seas, would pollute them, harming the ecosystem of the water bodies and making the water unfit for drinking or further use.

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

Answer:

Oils and fats are insoluble in water. When released in the drain, it causes hardening and blocking of the sewage pipes. In an open drain, the fats block the soil pores, which are required for filtering water. That is why oils and fats should not be released in the drain.

4. Describe the steps involved in getting clarified water from wastewater.

Answer:

The treatment of wastewater includes the following steps:

(i) First, the physical waste, like plastic, rags, pebbles, wood, etc., is removed by passing the water through a bar screen.

(ii) Then water is sent into the sand removal tank for removing sand, pebbles, grit, etc. through the process of sedimentation.

(iii) Then the rest of the solid waste is allowed to settle at the bottom of a large settling tank. This waste deposited at the bottom is called sludge and is removed through a scraper.

(iv) The harmful microorganisms in this water are killed through chlorination or UV rays.

(v) Through an aerator, air is pumped into this water so that aerobic bacteria can grow and decompose any remaining organic wastes.

(vi) This treated water is then released into the water bodies.

5. What is sludge? Explain how it is treated.

Answer:

Sludge is the solid waste that has settled at the bottom of settling tanks during the process of wastewater treatment.

It is treated by decomposition by anaerobic bacteria. This activated sludge further can be used as manure.

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

Answer:

Untreated human excreta contains many harmful organisms that can cause lots of health-related problems. It pollutes air, water, and soil. Epidemics like cholera, meningitis, etc., can be spread by untreated human excreta.

7. Name two chemicals used to disinfect water.

Answer:

Two chemicals used to disinfect water are chlorine and ozone.

8. Explain the function of bar screens in a wastewater treatment plant.

Answer:

Bar screens filter most of the large-sized solid waste like plastic, cans, wood, etc., from wastewater.

9. Explain the relationship between sanitation and disease.

Answer:

Sanitation refers to the availability of clean drinking water and proper treatment of human waste and sewage.

Without proper sanitation, various diseases like cholera, typhoid, diarrhea, etc. would spread. However, proper sanitation ensures that these diseases do not spread.

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

Answer:

As active citizens, we should ensure that proper sanitation facilities are available in our homes and workplaces, should make people aware of the necessity of sanitation, and should not throw garbage in the open, as it will block the drains and restrict the flow of the sewage.

11. Here is a crossword puzzle: Good luck!

Across
3 . Liquid waste products
4 . Solid waste extracted in sewage treatment
6 . A word related to hygiene
8 . The waste matter discharged from the human body
Down
1 . Used water
2 . A pipe carrying sewage
5 . Micro-organisms which causes cholera
7 . A chemical to disinfect water

Answer:

Across
3 . SEWAGE
4 . SLUDGE
6 . SANITATION
8 . EXCRETA
Down
1 . WASTEWATER
2 . SEWER
5 . BACTERIA
7 . OZONE

12. Study the following statements about ozone:

(a) It is essential for the breathing of living organisms.
(b) It is used to disinfect water.
(c) It absorbs ultraviolet rays.
(d) Its proportion in air is about 3%.

Which of these statements are correct?
(i) (a), (b), and (c)
(ii) (b) and (c)
(iii) (a) and (d)
(iv) All four

Answer:

(ii) (b) and (c) are correct.

Wastewater Story Class 7 Science Chapter 13-Topics

Wastewater Story
Water, Our Lifeline
What is Sewage
Water Freshness Up- Eventful Journey
Wastewater Treatment Plant (WWTP)
Better Housekeeping Practices
Sanitation And Diseases
Alternative Arrangement For Sewage Disposal
Sanitation in Public Places

Students can make their studies interesting through activities. For example, by visiting a sewage treatment plant, students can know how practically the plant is running and can relate to what they have studied in this chapter.

Chapter-wise NCERT Solutions of Class 7 Science

Chapter 1	Nutrition in Plants
Chapter 2	Nutrition in Animals
Chapter 4	Heat
Chapter 4	Acids, Bases and Salts
Chapter 5	Physical and Chemical Changes
Chapter 6	Respiration in Organisms
Chapter 7	Transportation in Animals and Plants
Chapter 8	Reproduction in Plants
Chapter 9	Motion and Time
Chapter 10	Electric Current and its Effects
Chapter 11	Light
Chapter 12	Forests: Our Lifeline
Chapter 13	Wastewater Story

Benefits of NCERT Solutions for Class 7 Science Chapter 13 Wastewater Story:

Class 7th Science Chapter 13 is important from the exam point of view.
One of the main aims of Wastewater Story is to create awareness about water usage.
The solutions for this chapter help to understand the concepts studied in the chapter well.
Along with the NCERT Solutions, doing the activities mentioned in the chapter will add to the advantage of understanding the chapter in depth.
It will help you score good marks in your school exam.
Class 7th Science Chapter 13 Solutions PDF is easy to download and use offline.
The questions and answers are prepared by subject experts as per the latest CBSE syllabus.

Also check,

Follow the links below to get your hands on the class 7 syllabus and the books related to it. You can also go through NCERT solutions for other subjects as well.

NCERT Books	NCERT Syllabus	NCERT solution Subject-wise
NCERT Books Class 7 Science	NCERT Syllabus Class 7 Science	NCERT Solutions for Class 7 Maths
NCERT Books Class 7	NCERT Syllabus Class 7	NCERT Solutions for Class 7 Science

Frequently Asked Questions (FAQs)

1. What is wastewater and where does it come from?

Wastewater is any water that has been affected by human use and is no longer pure. It includes water from household activities like washing, bathing, and toilets, as well as water from industrial and commercial processes.

2. What are some common contaminants found in wastewater?

Common contaminants found in wastewater include human waste, chemicals, pharmaceuticals, heavy metals, and nutrients like nitrogen and phosphorus.

3. How can wastewater be reused?

Wastewater can be treated and reused for a variety of purposes, such as irrigation, industrial processes, and even drinking water in some cases. This helps to conserve water and reduce the demand for fresh water.

4. What are the consequences of untreated wastewater being released into the environment?

Untreated wastewater can have serious consequences for the environment and public health. It can contaminate water sources, harm aquatic life, and spread diseases. It can also lead to the growth of harmful algal blooms, which can have negative impacts on the economy and tourism.

5. How can individuals help to protect water resources and reduce the impact of wastewater?

Individuals can help to protect water resources and reduce the impact of wastewater by using water efficiently, properly disposing of household hazardous waste, supporting policies and regulations that protect water resources, and participating in local water conservation efforts.

Also Read

NCERT Solutions for Class 7 Science Chapter 13 Motion and Time

NCERT Solutions for Class 7 Science Chapter 14 Electric Current and Its Effects

NCERT Solutions for Class 7 Science Chapter 5 Acids Bases and Salts

NCERT Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes

NCERT Solutions for Class 7 Science Chapter 18 Wastewater Story

NCERT Solutions for Class 7 Science Chapter 4 Heat

NCERT Books for Class 7 English 2025-26: Download PDF

NCERT Books for Class 7 Social Science 2025-26: Download PDF here

NCERT Books for Class 7 Science 2025-26: Download PDF Here

NCERT Books for Class 7 All Subjects: Download PDF

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Popular Questions

A block of mass 0.50 kg is moving with a speed of 2.00 ms^-1 on a smooth surface. It strikes another mass of 1.00 kg and then they move together as a single body. The energy loss during the collision is

Option 1) $0.34\; J$	Option 2) $0.16\; J$
Option 3) $1.00\; J$	Option 4) $0.67\; J$

A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1 m 1000 times. Assume that the potential energy lost each time he lowers the mass is dissipated. How much fat will he use up considering the work done only when the weight is lifted up ? Fat supplies 3.8×10⁷J of energy per kg which is converted to mechanical energy with a 20% efficiency rate. Take g = 9.8 ms⁻² :

Option 1)

2.45×10⁻³ kg

Option 2)

6.45×10⁻³ kg

Option 3)

9.89×10⁻³ kg

Option 4)

12.89×10⁻³ kg

An athlete in the olympic games covers a distance of 100 m in 10 s. His kinetic energy can be estimated to be in the range

Option 1) $2,000 \; J - 5,000\; J$	Option 2) $200 \, \, J - 500 \, \, J$
Option 3) $2\times 10^{5}J-3\times 10^{5}J$	Option 4) $20,000 \, \, J - 50,000 \, \, J$

A particle is projected at 60⁰ to the horizontal with a kinetic energy $K$ . The kinetic energy at the highest point

Option 1) $K/2\,$	Option 2) $\; K\;$
Option 3) $zero\;$	Option 4) $K/4$

In the reaction,

$2Al_{(s)}+6HCL_{(aq)}\rightarrow 2Al^{3+}\, _{(aq)}+6Cl^{-}\, _{(aq)}+3H_{2(g)}$

Option 1) $11.2\, L\, H_{2(g)}$ at STP is produced for every mole $HCL_{(aq)}$ consumed	Option 2) $6L\, HCl_{(aq)}$ is consumed for ever $3L\, H_{2(g)}$ produced
Option 3) $33.6 L\, H_{2(g)}$ is produced regardless of temperature and pressure for every mole Al that reacts	Option 4) $67.2\, L\, H_{2(g)}$ at STP is produced for every mole Al that reacts .

How many moles of magnesium phosphate, $Mg_{3}(PO_{4})_{2}$ will contain 0.25 mole of oxygen atoms?

Option 1) 0.02	Option 2) 3.125 × 10^-2
Option 3) 1.25 × 10^-2	Option 4) 2.5 × 10^-2

If we consider that 1/6, in place of 1/12, mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will

Option 1) decrease twice	Option 2) increase two fold
Option 3) remain unchanged	Option 4) be a function of the molecular mass of the substance.

With increase of temperature, which of these changes?

Option 1) Molality	Option 2) Weight fraction of solute
Option 3) Fraction of solute present in water	Option 4) Mole fraction.

Number of atoms in 558.5 gram Fe (at. wt.of Fe = 55.85 g mol^-1) is

Option 1) twice that in 60 g carbon	Option 2) 6.023 × 10²²
Option 3) half that in 8 g He	Option 4) 558.5 × 6.023 × 10²³

A pulley of radius 2 m is rotated about its axis by a force F = (20t - 5t²) newton (where t is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is 10 kg m² , the number of rotations made by the pulley before its direction of motion if reversed, is