3. Water Pollution

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CSS GSA — Paper 7, Part-I, Section III, Sub-topic 3: Water Pollution

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Past-paper weightage: moderate to high. Eutrophication, oxygen-demanding wastes and drinking-water standards come up regularly.

1. What Is Water Pollution

• Water pollution: contamination of rivers, lakes, groundwater and oceans by harmful substances, making water unsafe or unusable and harming ecosystems
• Causes
  • Industrial discharge
  • Agricultural runoff (fertilizers, pesticides)
  • Untreated sewage
  • Oil spills
  • Plastic and solid waste dumping
  • Mining

2. Major Water Pollutants

3. Drinking Water Quality and Standards

• Parameters checked: pH, turbidity, dissolved oxygen, coliform bacteria, heavy metals
• Standards
  • WHO guidelines are the global reference
  • In Pakistan, national standards and the PSQCA apply
• Measurement methods
  • Microbial: coliform count
  • Chemical: heavy metals, nitrates, pH
  • Physical: turbidity, colour, odour

4. Water-Logging (Pakistan Context)

• Meaning: the water table rises close to the surface, saturating the root zone
• Main reasons in Pakistan
  • Over-irrigation with poor natural drainage
  • Seepage from unlined canals
  • Flat Indus plain, which slows runoff
  • Rising groundwater in irrigated areas without enough drainage

5. MCQ Traps

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• BOD = oxygen used by microbes to break down organic waste; high BOD = polluted water
• Eutrophication is driven by excess nitrogen and phosphorus, not heavy metals

6. Self-Test Questions

1. What is 'Water Pollution'? Discuss its causes and measurement methods.
2. Discuss the major types of water pollutants, and name the countries with the highest and lowest percentage of it.
3. Briefly explain the main reasons of water-logging in Pakistan.
4. What is eutrophication, and which pollutant category causes it?

7. Past-Paper MCQs (FPSC)

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The FPSC MCQ papers you shared (2024 and 2025) had no direct question on water pollution.

8. Past-Paper Long Questions with Answers (FPSC)

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Every question below appeared in the FPSC papers you shared; the year and question number are in each title. Answers are model outlines written by me, ready to expand.

• CSS 2018 Q4(B), 2025 Q4(b): What is water pollution? Discuss its causes and measurement methods. How is it produced, and what part do bacteria play after a river is polluted by sewage? Name the countries with the highest and lowest percentage. (5)

  • Water pollution: see section 1; causes: industry, sewage, agricultural runoff, oil spills, plastics
  • Measurement: pH, turbidity, DO, BOD, TDS, coliform count, heavy metals
  • Role of bacteria after sewage enters a river
    1. Aerobic bacteria break down the organic waste and use up dissolved oxygen (rising BOD)
    2. Oxygen falls; fish and other aerobic life die
    3. Anaerobic bacteria then take over, producing foul gases (methane, hydrogen sulphide) and a bad smell
    4. Disease-causing bacteria in the sewage (cholera, typhoid) spread waterborne illness
    5. Plant nutrients released cause algal blooms (eutrophication)
    6. The river slowly recovers downstream by self-purification if the load is small
  • Highest and lowest: there is no single official ranking; water pollution is commonly reported as worst in parts of South Asia and sub-Saharan Africa (e.g. India, Bangladesh) and best in countries with strong treatment systems such as Finland, Norway and Switzerland. Quote it as 'commonly reported'

• CSS 2022 Q4(a), 2024 Q4(c): Define water pollution. What indicators measure water quality? Write the drinking water quality standards. How do heavy metals in water affect living organisms? (5)

  Indicator	Healthy / standard value
  pH	6.5–8.5
  Dissolved oxygen (DO)	High is good
  BOD	Low is good
  Total dissolved solids (TDS)	Generally under 500–1,000 mg/L
  Coliform bacteria	Zero in drinking water
  Heavy metals (arsenic, lead)	Strict limits (arsenic WHO guideline 10 µg/L)

  • Heavy metals enter water from industry, mining and pesticides; they do not break down and bioaccumulate
    • Lead: nervous system and child brain development
    • Arsenic: skin lesions and cancers
    • Mercury: nervous system and kidneys
    • Cadmium: kidneys and bones

• CSS 2023 Q4(b): What is the role of oxygen-demanding wastes in water pollution? How can it be prevented? (5)

  • Oxygen-demanding wastes: organic matter (sewage, food waste, manure) that aerobic bacteria decompose, consuming dissolved oxygen
  • Measured as BOD: more waste, higher BOD, less oxygen
  • Effects: fish suffocate; only pollution-tolerant species (some worms and bacteria) survive; ecosystem collapses
  • Prevention: sewage and effluent treatment plants, cut agricultural runoff, enforce discharge limits, composting and waste reduction

• CSS 2017 Q2(b): Briefly explain the main reasons for water-logging in Pakistan. (5)

  • Reasons: canal seepage (unlined canals), over-irrigation, poor drainage, flat topography, rising water table
  • Linked problem: salinity, as evaporation leaves salts at the surface
  • Remedies: tube wells and drainage (SCARP projects), canal lining, drip and sprinkler irrigation, salt-tolerant crops

9. CSS Exam Perspective

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• Most repeated areas: causes and indicators of water pollution, oxygen-demanding wastes/BOD, drinking-water standards, heavy metals, water-logging
• Short-question style: 'Define… What indicators…?', 'Explain how… is produced'
• Tip: give a small indicator table (pH, DO, BOD, TDS, coliform) in any water-quality answer