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CBSE Class 7 Science Chapter 13 Wastewater Story Worksheet with Answers

Chapter 13 Wastewater Story in NCERT Class 7 Science explores the journey of water after we use it — from our homes through drains to treatment plants and back to nature. This printable worksheet tests your understanding of sewage composition, treatment processes, sanitation challenges, and eco-friendly practices. Complete the five sections in 60 minutes to master this crucial environmental topic that appears regularly in CBSE term exams and lays the foundation for Class 9-10 environmental science.

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Key takeaways

  • ✓Sewage is wastewater released from homes, industries, hospitals and other buildings, containing organic and inorganic impurities
  • ✓Wastewater treatment involves physical removal of large objects, bacterial decomposition of organic matter, and chemical disinfection before release
  • ✓Open drains and untreated sewage spread water-borne diseases like cholera, typhoid, hepatitis and dysentery in communities
  • ✓Vermicomposting uses redworms to convert kitchen waste into nutrient-rich compost, reducing organic load on sewage systems
  • ✓Better housekeeping practices like avoiding cooking oil disposal in drains and minimizing water wastage reduce sewage generation significantly

Quick Chapter Recap: Wastewater Story

Before attempting the worksheet, refresh these core ideas from Chapter 13. Wastewater or sewage is the used water from homes, industries, hospitals and agricultural fields that flows through underground pipes called sewers. It contains dissolved and suspended impurities — organic waste like human excreta and kitchen waste, plus inorganic substances like phosphates, nitrates and metals. Wastewater treatment plants clean this water in three stages: primary treatment removes large solids by screening and sedimentation; secondary treatment uses aerobic bacteria to decompose organic matter in aeration tanks; tertiary treatment disinfects water with chlorine or UV before releasing it into water bodies. Poor sanitation and open drains allow pathogens to contaminate drinking water sources, causing diseases. Simple actions like proper garbage disposal, avoiding cooking oil in drains, and using less water reduce sewage volume and protect both treatment systems and the environment.
  • Sewage = wastewater from various sources containing organic and inorganic impurities
  • Treatment stages: physical removal → bacterial decomposition → chemical disinfection
  • Sludge from treatment can be converted to biogas or used as manure after digestion
  • Water-borne diseases spread through contaminated water: cholera, typhoid, hepatitis, dysentery
  • Vermicomposting, minimizing waste, and water conservation are better housekeeping practices

Worksheet Information and Instructions

This worksheet is structured to progressively test your knowledge from recall to application and analysis. Difficulty Level: Moderate, aligned with CBSE Class 7 term examination pattern. Suggested Time: 60 minutes for completion, plus 15 minutes for self-checking against the answer key. The question distribution mirrors typical CBSE Science papers: objective questions (MCQs and fill-ins) carry 1 mark each, short answers 2-3 marks, and long answers or HOTS questions 5 marks. Attempt all sections in order. For short and long answers, use diagrams where asked and write in complete sentences. The case study at the end integrates real-world scenarios exactly as seen in recent CBSE papers. Use the answer key not just to mark correct or wrong, but to understand the reasoning behind each answer and fill gaps in your preparation.
  • Total sections: Five (A to E) plus one case-study question and complete answer key
  • Question types: MCQs, fill-in-the-blanks, matching, short answer (2-3 marks), long answer (5 marks)
  • Materials needed: printed worksheet, pen, pencil for diagrams, eraser
  • Marking scheme provided in answer key for self-assessment
  • Review NCERT Class 7 Science Chapter 13 textbook pages 151-162 before attempting

Section A: Multiple Choice Questions (1 mark each)

Choose the single best answer for each question. These MCQs test your conceptual clarity on sewage composition, treatment stages, and sanitation practices covered in the NCERT textbook. Each question has four options; select the most accurate one based on Chapter 13 content. Write the question number and your chosen option letter clearly. No negative marking, so attempt every question even if unsure. These questions typically appear in the first section of CBSE Class 7 Science term exams and form the foundation for higher-order questions that follow in later sections of this worksheet.
  • Q1. Which of the following is NOT a component of sewage? (a) Organic waste (b) Nutrients like phosphates (c) Dissolved oxygen (d) Suspended solids
  • Q2. The process in which aerobic bacteria decompose organic matter in wastewater is called: (a) Primary treatment (b) Sedimentation (c) Activated sludge process (d) Screening
  • Q3. Wastewater from a house enters the treatment plant through: (a) Open drains (b) Sewers (c) Septic tanks (d) Vermicomposting pits
  • Q4. Biogas obtained from sludge digestion mainly contains: (a) Oxygen and nitrogen (b) Methane and carbon dioxide (c) Hydrogen and helium (d) Chlorine and fluorine
  • Q5. Which disease is NOT caused by contaminated water? (a) Cholera (b) Typhoid (c) Tuberculosis (d) Dysentery
  • Q6. Vermicomposting uses which organism to convert kitchen waste into compost? (a) Earthworms (b) Bacteria (c) Algae (d) Fungi

Section B: Fill in the Blanks (1 mark each)

Complete each sentence with the appropriate term from Chapter 13. These questions test your recall of key vocabulary and definitions related to wastewater treatment and sanitation. Write only the missing word or phrase in your answer sheet against the question number. Spelling must be accurate as per NCERT terminology. The blanks cover processes, components, and practices discussed across all sections of the Wastewater Story chapter. Review technical terms like sludge, aeration, contaminants, and inorganic impurities before filling these in. Such questions are common in CBSE Class 7 Science worksheets and formative assessments conducted by schools.
  • Q7. Wastewater released from homes, industries and hospitals is called _________.
  • Q8. The solid waste that settles down during wastewater treatment is called _________.
  • Q9. _________ are the underground pipes that carry wastewater from homes to treatment plants.
  • Q10. Chemical used to disinfect water in the final stage of treatment is _________.
  • Q11. The practice of keeping our surroundings clean and hygienic is known as _________.

Section C: Match the Following and True/False (1 mark each)

This section includes two sub-parts. Part I requires matching items in Column A with their correct descriptions in Column B, focusing on wastewater treatment stages and their purposes. Write the correct pairs (e.g., 1-d, 2-a) in your answer sheet. Part II presents five statements about sewage, sanitation and water pollution; mark each as True or False. If false, you may briefly write the correct statement for bonus understanding, though marks are awarded only for the True/False identification. These question types assess both your factual knowledge and ability to distinguish correct information from misconceptions — a skill tested in CBSE practical and theory exams alike.
  • Part I - Match the Following:
  • Column A: (1) Bar screens (2) Aeration tank (3) Chlorination (4) Sludge digestion
  • Column B: (a) Kills disease-causing bacteria (b) Removes large solid objects (c) Produces biogas (d) Aerobic bacteria break down organic waste
  • Part II - True or False:
  • Q12. Open drains are a safe way to dispose of wastewater. (True/False)
  • Q13. Wastewater treatment converts polluted water into drinking water. (True/False)
  • Q14. Cooking oil and fats should be thrown into kitchen sinks. (True/False)
  • Q15. Vermicomposting reduces the load on sewage treatment plants. (True/False)
  • Q16. Chemicals and medicines should be poured down the drain when expired. (True/False)

Section D: Short Answer Questions (2-3 marks each)

Answer each question in 30-40 words. These questions require you to explain concepts, describe processes, or list points with brief reasoning. Marks are awarded for accuracy, clarity, and completeness. Use scientific terminology from NCERT Class 7 Science Chapter 13. Where a question asks for a diagram or flowchart, draw it neatly with labels; marks are split between the diagram and written explanation. Short-answer questions form a significant portion of CBSE Class 7 term exams and test your ability to articulate understanding beyond mere recall. Reference specific treatment stages, organisms, or practices to score full marks.
  • Q17. What is sewage? Mention any two types of impurities present in it. (2 marks)
  • Q18. Explain the role of bacteria in wastewater treatment. (2 marks)
  • Q19. Why should we avoid throwing cooking oil and fats down the drain? Give two reasons. (2 marks)
  • Q20. What is sludge? How is it utilized beneficially after treatment? (3 marks)
  • Q21. Draw a simple flowchart showing the three main stages of wastewater treatment. (3 marks)

Section E: Long Answer and HOTS Questions (5 marks each)

These questions demand detailed explanations, application of concepts to new situations, or analysis of environmental issues. Allocate 80-100 words per answer. Marks are awarded for depth of understanding, logical flow, use of examples, and inclusion of diagrams where relevant. HOTS (Higher Order Thinking Skills) questions test your ability to connect the Wastewater Story with real-life sanitation challenges in Indian cities and villages. Reference the NCERT discussion on better housekeeping practices, disease prevention, and alternative sanitation solutions. Such questions prepare you for the analytical and application-based items increasingly seen in CBSE Class 7 Science examinations and lay groundwork for environmental studies in higher classes.
  • Q22. Describe the process of wastewater treatment in a municipal treatment plant. Explain the role of each stage in removing different types of impurities. (5 marks)
  • Q23. Poor sanitation and open drains lead to the spread of diseases. Explain this statement with examples of water-borne diseases and suggest three measures to improve sanitation in your locality. (5 marks)
  • Q24. 'Every individual can contribute to reducing the problem of wastewater.' Justify this statement by explaining at least four better housekeeping practices mentioned in Chapter 13. (5 marks)

Case-Study Based Question (4 marks)

Read the scenario below carefully and answer the sub-questions that follow. Case-study questions integrate multiple concepts from the chapter and test your ability to apply knowledge to realistic situations. This format mirrors the competency-based questions now standard in CBSE Class 7 Science papers. Marks are distributed across sub-parts, so answer each part distinctly. Use information from the passage as well as your Chapter 13 understanding. Such questions develop critical thinking and data interpretation skills essential for higher secondary science courses. Scenario: Greenfield Society in Pune noticed foul smell and mosquito breeding around an open drain carrying wastewater from 200 households. The municipal corporation proposed constructing a small decentralized wastewater treatment plant and requested residents to adopt better waste disposal habits.
  • Q25(a). Identify two health hazards the residents face due to the open drain. (1 mark)
  • Q25(b). Explain how a wastewater treatment plant will solve the problem of foul smell. (1 mark)
  • Q25(c). Suggest two better housekeeping practices residents should follow to reduce the load on the treatment plant. (2 marks)

Complete Answer Key with Explanations

Use this section to check your responses after completing all sections. Each answer includes a brief explanation to help you understand the concept, not just memorize the answer. Award yourself marks honestly and note topics where you lost marks for focused revision. For MCQs and fill-ins, answers are direct. For short and long answers, compare key points — if you covered the main ideas with correct terminology, award full marks even if wording differs slightly. The explanations reference NCERT page numbers and key terms to guide further reading. Self-assessment builds exam confidence and highlights weak areas. Revisit those sections in the NCERT Class 7 Science textbook and consider solving additional worksheets. Platforms like CBSETUTOR.ai offer 24×7 AI-powered doubt solving where you can upload your worksheet answers via photo and receive instant feedback, all for ₹999/month covering all subjects for Classes 6-12, with a 3-day free trial to start.
  • Section A — MCQs: Correct options with reasoning for each
  • Section B — Fill-in-the-Blanks: Accurate technical terms as per NCERT
  • Section C — Matching and True/False: Paired correctly and validity explained
  • Section D — Short Answers: Model answers with key points highlighted
  • Section E — Long Answers & Case Study: Detailed responses with mark distribution shown

Answer Key: Section A (MCQs)

A1. (c) Dissolved oxygen — Sewage contains organic waste, inorganic impurities like phosphates and nitrates, and suspended solids. However, it has very low or negligible dissolved oxygen because aerobic bacteria consume available oxygen while decomposing organic pollutants, making water oxygen-deficient. A2. (c) Activated sludge process — This is part of secondary treatment where air is pumped into aeration tanks. Aerobic bacteria thrive in this oxygen-rich environment and decompose organic matter present in wastewater, significantly reducing the biological oxygen demand (BOD). A3. (b) Sewers — These are underground closed pipes that transport wastewater from homes, industries and other buildings to the treatment plant. Open drains expose wastewater to the environment and cause pollution; septic tanks are on-site treatment, not transport. A4. (b) Methane and carbon dioxide — During anaerobic digestion of sludge, bacteria break down organic matter in the absence of oxygen, producing biogas consisting mainly of methane (50-70%) and carbon dioxide, along with traces of hydrogen sulfide. A5. (c) Tuberculosis — Cholera, typhoid and dysentery are water-borne diseases spread through contaminated drinking water containing pathogens from sewage. Tuberculosis is an airborne disease caused by bacteria spreading through droplets when an infected person coughs or sneezes. A6. (a) Earthworms — Vermicomposting specifically uses redworms or earthworms (species like Eisenia fetida) that consume kitchen waste, decompose it, and excrete nutrient-rich castings that form excellent compost for plants, reducing organic waste load.

Answer Key: Sections B and C

Section B — Fill in the Blanks: A7. sewage (or wastewater) — The used water from various sources containing impurities is termed sewage or wastewater. A8. sludge — Solid waste and semi-solid waste that settles at the bottom of sedimentation tanks during primary and secondary treatment is called sludge. A9. Sewers — These underground pipes carry wastewater from buildings to treatment facilities, keeping it enclosed and preventing environmental contamination. A10. chlorine (or bleaching powder/UV) — Chlorination is the common disinfection method; chlorine kills bacteria and pathogens in treated water before release. A11. sanitation — Proper sanitation includes safe disposal of human waste, clean drinking water supply, and hygienic living conditions to prevent diseases. Section C — Part I Matching: 1-b (Bar screens remove large solid objects), 2-d (Aeration tank is where aerobic bacteria break down organic waste), 3-a (Chlorination kills disease-causing bacteria), 4-c (Sludge digestion produces biogas). Part II True/False: A12. False — Open drains spread diseases, attract pests, and contaminate groundwater. A13. False — Treatment makes water clean enough to release into environment, but it is not made potable (drinkable) without further purification. A14. False — Oil and fats clog pipes and hinder bacterial action in treatment plants; they should be collected separately. A15. True — Composting kitchen waste at home reduces organic matter entering sewage systems. A16. False — Chemicals harm bacteria in treatment plants and pollute water bodies; dispose them at designated collection points.

Answer Key: Sections D, E and Case Study

A17. Sewage is wastewater released from homes, industries, hospitals and agricultural fields. Two impurities: (i) Organic impurities like human excreta, food waste, soap, detergent. (ii) Inorganic impurities like nitrates, phosphates, metals. (2 marks: 1 for definition, 1 for two types). A18. Aerobic bacteria decompose organic matter in wastewater during secondary treatment, converting it into simpler, harmless substances. Anaerobic bacteria digest sludge to produce biogas. This biological treatment is eco-friendly and cost-effective. (2 marks). A19. (i) Oil and fats clog drainage pipes, leading to blockages and overflow. (ii) They hinder the action of bacteria in treatment plants, reducing treatment efficiency and polluting water bodies. (2 marks). A20. Sludge is the solid/semi-solid waste that settles during wastewater treatment. It is digested anaerobically by bacteria to produce biogas (used as fuel) and the remaining digested sludge is dried and used as manure for agriculture. (3 marks: 1 for definition, 2 for utilization). A21. Flowchart: Wastewater → Primary Treatment (screening, sedimentation) → Secondary Treatment (aeration, bacterial decomposition) → Tertiary Treatment (disinfection with chlorine) → Treated water released. (3 marks: 1 per stage with correct sequence). A22. Wastewater treatment involves three stages. Primary: Bar screens remove floating debris; grit and sand settle in chambers, reducing suspended solids. Secondary: Wastewater enters aeration tanks where air is bubbled; aerobic bacteria digest organic waste, lowering BOD. Activated sludge is separated. Tertiary: Chlorine is added to kill pathogens; UV may also be used. Treated water is clear and safe for rivers. Sludge is digested anaerobically to yield biogas and manure. (5 marks: stages explained with processes and outcomes). A23. Open drains and poor sanitation allow human waste and garbage to contaminate drinking water sources, spreading diseases like cholera (severe diarrhea), typhoid (high fever, intestinal infection), hepatitis (liver infection), and dysentery. Measures: (i) Construct covered sewers and treatment plants. (ii) Ensure safe drinking water supply, separate from drainage. (iii) Promote toilets, end open defecation, and enforce waste segregation rules. (5 marks). A24. Individuals reduce wastewater problems by: (i) Not throwing cooking oil, fats into sinks; collect and dispose properly. (ii) Avoiding disposal of chemicals, medicines, sanitary waste in drains; use dustbins. (iii) Minimizing water use during bathing, washing to reduce sewage volume. (iv) Vermicomposting kitchen waste instead of washing it down drains, reducing organic load. These practices protect treatment plants, save water, and reduce pollution. (5 marks). Case Study A25(a): (i) Spread of water-borne diseases like cholera, dysentery due to contaminated water. (ii) Mosquito breeding causing malaria and dengue. (1 mark). A25(b): Treatment plant will decompose organic waste using bacteria, eliminating rotting matter that causes smell, and disinfect water, preventing anaerobic decomposition. (1 mark). A25(c): (i) Do not throw garbage, plastic, food waste into drains. (ii) Avoid pouring oil, fats, chemicals down sinks; collect and dispose responsibly. (2 marks).

Frequently asked questions

What is the purpose of this CBSE Class 7 Science Chapter 13 worksheet?+
This worksheet provides comprehensive practice on the Wastewater Story chapter, covering sewage composition, treatment processes, sanitation and disease prevention. It prepares students for term exams through varied question types with a complete answer key for self-assessment and concept reinforcement.
How much time should a Class 7 student take to complete this worksheet?+
The suggested time is 60 minutes to attempt all sections under exam-like conditions. Allow an additional 15 minutes to review your answers against the provided answer key and understand any mistakes or gaps in your responses.
Are the questions in this worksheet based on the latest CBSE syllabus?+
Yes, all questions are aligned with the current NCERT Class 7 Science syllabus and textbook content for Chapter 13. The worksheet follows CBSE exam patterns including MCQs, short answers, long answers, and case-study questions seen in recent term assessments.
What topics from Wastewater Story are covered in the worksheet?+
The worksheet covers sewage sources and composition, primary secondary and tertiary treatment stages, role of bacteria, sludge management and biogas production, water-borne diseases, sanitation practices, and better housekeeping habits like vermicomposting and waste minimization.
Can I use this worksheet for exam preparation and revision?+
Absolutely. This worksheet is designed for both practice and revision. Attempt it after studying Chapter 13, then use the detailed answer key to identify weak areas. Revisit those NCERT sections and re-attempt questions to strengthen understanding before school tests or term exams.
How should I use the answer key provided in this worksheet?+
Complete all sections first without looking at answers. Then check each response against the answer key, which includes explanations and mark allocation. Note topics where you lost marks and review those in your NCERT textbook. Self-assessment builds confidence and exam readiness.
What is the difficulty level of this Class 7 Science worksheet?+
The worksheet is of moderate difficulty, matching typical CBSE Class 7 term exam standards. It includes a mix of easy recall questions (MCQs, fill-ins), moderate application questions (short answers), and challenging HOTS questions to develop higher-order thinking skills required in competitive and board exams.
Where can I get additional help if I am stuck on worksheet questions?+
If you find questions challenging, review NCERT Class 7 Science Chapter 13 pages 151-162 carefully. For instant doubt clearing, platforms like CBSETUTOR.ai offer 24×7 AI tutoring where you upload your worksheet via photo and receive step-by-step solutions, all for ₹999/month across Classes 6-12 with a 3-day free trial.
How many marks is each section in this worksheet worth?+
Section A MCQs carry 1 mark each (6 marks total), Section B fill-ins 1 mark each (5 marks), Section C matching/true-false 1 mark each (about 5 marks), Section D short answers 2-3 marks each (about 12 marks), Section E long answers 5 marks each (15 marks), and the case study 4 marks, totaling approximately 47 marks.
Does this worksheet include diagrams and flowcharts as asked in CBSE exams?+
Yes, Section D includes a question asking for a flowchart of wastewater treatment stages. The answer key provides a sample diagram. Drawing neat, labeled diagrams is essential in CBSE Science exams, and this worksheet helps you practice that skill alongside written answers.

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