Water Pollution — Types, BOD/COD, Eutrophication, Water Treatment, and Jal Jeevan Mission

Water pollution is a critical topic for PSC exams, covering both science fundamentals (BOD, COD, eutrophication) and current affairs (Jal Jeevan Mission, Namami Gange). Expect 1-2 questions in every Graduate Level paper.

1. What is Water Pollution?

Aspect	Detail
Definition	Contamination of water bodies (rivers, lakes, groundwater, oceans) by harmful substances that degrade water quality
Key law in India	Water (Prevention and Control of Pollution) Act, 1974
Enforcing body	Central Pollution Control Board (CPCB) and State Pollution Control Boards (SPCBs)
CPCB established	1974 under the Water Act

2. Types of Water Pollution

Type	Source	Examples
Organic pollution	Sewage, agricultural waste, food processing	Decomposition consumes dissolved oxygen; raises BOD
Chemical pollution	Industrial effluents, pesticides, fertilisers	Heavy metals (mercury, lead, arsenic, cadmium), acids, alkalis
Thermal pollution	Power plants, industrial cooling water	Hot water discharge raises water temperature; reduces dissolved oxygen
Nutrient pollution	Agricultural runoff (fertilisers), sewage	Excess nitrogen and phosphorus cause eutrophication
Microbial/biological pollution	Untreated sewage, animal waste	Bacteria (E. coli, cholera), viruses, parasites
Radioactive pollution	Nuclear plants, medical waste	Radioactive isotopes contaminate water
Sediment pollution	Construction, deforestation, mining	Soil particles cloud water; destroy aquatic habitats
Oil pollution	Oil spills, shipping, refineries	Oil slicks on water surface; toxic to marine life
Plastic/microplastic pollution	Plastic waste, synthetic fibres	Persist in water for centuries; enter food chain

3. BOD and COD — Core Concepts

BOD (Biochemical Oxygen Demand)

Aspect	Detail
Definition	Amount of dissolved oxygen required by aerobic microorganisms to break down organic matter in a water sample over 5 days at 20 degrees C
Unit	mg/L (milligrams per litre) or ppm (parts per million)
Clean water BOD	Below 1 mg/L
Moderately polluted	3-5 mg/L
Heavily polluted	Above 8 mg/L
Raw sewage BOD	200-600 mg/L
Significance	Higher BOD = more organic pollution = less oxygen for aquatic life

COD (Chemical Oxygen Demand)

Aspect	Detail
Definition	Amount of oxygen required to chemically oxidise ALL organic and inorganic matter in water (using a strong chemical oxidant like potassium dichromate)
Unit	mg/L
Difference from BOD	COD measures total oxygen demand (both biodegradable and non-biodegradable); always higher than or equal to BOD
Significance	Faster test than BOD (2-3 hours vs 5 days); indicates total pollution load

BOD vs COD Comparison

Parameter	BOD	COD
Measures	Biodegradable organic matter only	All organic + some inorganic matter
Method	Biological (microbial decomposition)	Chemical (strong oxidant)
Time required	5 days	2-3 hours
Value	Always lower than or equal to COD	Always higher than or equal to BOD
Use	Assessing organic pollution in natural water	Industrial effluent monitoring

PSC Favourite: “BOD stands for?” — Biochemical Oxygen Demand. “Higher BOD means?” — More polluted water.

4. Dissolved Oxygen (DO)

Aspect	Detail
Definition	Amount of oxygen dissolved in water; essential for aquatic life
Healthy water DO	6-8 mg/L or above
Fish survival minimum	4-5 mg/L (below this, fish die)
Zero DO	Anaerobic conditions; hydrogen sulphide produced (foul smell)
Factors affecting DO	Temperature (cold water holds more DO), aeration, pollution (pollution reduces DO)

5. Eutrophication

Aspect	Detail
Definition	Excessive enrichment of a water body with nutrients (nitrogen and phosphorus), leading to dense plant/algae growth and oxygen depletion
Cause	Agricultural fertiliser runoff, sewage, detergents (phosphates)
Process	Nutrients enter water body, causing algal bloom, blocking sunlight, algae die and decompose, decomposition consumes dissolved oxygen, creating a “dead zone”
Algal bloom	Rapid, excessive growth of algae on the water surface
Dead zone	Area with very low or zero dissolved oxygen (hypoxia); aquatic life dies
Example in India	Vembanad Lake (Kerala), Chilika Lake (Odisha), Dal Lake (J and K)
Prevention	Reduce fertiliser use, treat sewage before discharge, ban phosphate detergents

Eutrophication Process (Step-by-Step)

Step	What Happens
1	Excess nutrients (N, P) enter the water body from farms, sewage
2	Algae and aquatic plants grow rapidly (algal bloom)
3	Algal bloom blocks sunlight from reaching deeper plants
4	Submerged plants die due to lack of sunlight
5	Algae also die after their short lifecycle
6	Decomposition of dead organic matter by bacteria consumes dissolved oxygen
7	Dissolved oxygen drops drastically (hypoxia)
8	Fish and aquatic animals die (“fish kill”)
9	Water becomes murky, foul-smelling, and unusable

6. Water Treatment — Stages

Drinking Water Treatment

Stage	Process	Purpose
1. Screening	Passing water through screens	Remove large debris (leaves, sticks, plastic)
2. Coagulation/Flocculation	Adding coagulants (alum, ferric chloride)	Suspended particles clump together (flocs)
3. Sedimentation	Allowing flocs to settle	Remove suspended solids
4. Filtration	Passing through sand/gravel/activated carbon filters	Remove fine particles, some bacteria
5. Disinfection	Adding chlorine, ozone, or UV treatment	Kill bacteria, viruses, parasites
6. Storage and distribution	Storing in clean tanks, piped supply	Safe drinking water to households

Sewage/Wastewater Treatment

Stage	Process	Detail
Primary treatment	Physical processes	Screening, sedimentation; removes about 60% of suspended solids
Secondary treatment	Biological processes	Activated sludge process, trickling filters; microbes decompose organic matter; removes about 90% of organic matter
Tertiary treatment	Advanced processes	Nutrient removal (N, P), chemical disinfection, membrane filtration; produces high-quality effluent

Key Water Treatment Terms

Term	Meaning
Chlorination	Adding chlorine to kill pathogens — most common disinfection method
Reverse Osmosis (RO)	Membrane technology that removes dissolved salts and contaminants
UV treatment	Ultraviolet light kills microorganisms without chemicals
Ozonation	Using ozone gas for disinfection; more effective than chlorine but costlier
Activated carbon	Adsorbs organic pollutants, pesticides, and removes odour
Fluoridation	Adding fluoride to water to prevent dental decay (controversial)
Defluoridation	Removing excess fluoride (Nalgonda technique — developed in India)

7. Water Pollution-Related Diseases

Disease	Pollutant/Cause	Detail
Cholera	Vibrio cholerae in contaminated water	Severe diarrhoea
Typhoid	Salmonella typhi	Contaminated water/food
Hepatitis A and E	Virus in sewage-contaminated water	Jaundice, liver damage
Arsenicosis	Arsenic in groundwater	Skin lesions, cancer; West Bengal, Bihar
Fluorosis	Excess fluoride in groundwater	Dental and skeletal fluorosis; Rajasthan, Andhra Pradesh, Gujarat
Minamata disease	Mercury poisoning	Neurological damage; named after Minamata, Japan
Itai-itai disease	Cadmium poisoning	Bone softening and pain; named after Toyama, Japan
Blue Baby Syndrome (Methemoglobinemia)	Excess nitrate in water	Affects infants; nitrate interferes with oxygen transport
Lead poisoning	Lead in old pipes/paint	Neurological damage, especially in children

PSC Favourite: “Minamata disease is caused by?” — Mercury poisoning. “Itai-itai disease is caused by?” — Cadmium poisoning.

8. Jal Jeevan Mission (JJM)

Aspect	Detail
Launched	15 August 2019 (announced by PM Modi)
Full name	Jal Jeevan Mission — Har Ghar Jal
Objective	Provide Functional Household Tap Connection (FHTC) to every rural household by 2024
Target	19.35 crore rural households
Water supply standard	55 litres per person per day (lpcd) of potable water
Total outlay	Rs. 3.60 lakh crore
Implementing ministry	Ministry of Jal Shakti
Progress (2024)	Over 14.8 crore tap connections provided (76%+ coverage)
Goa and Dadra-Nagar Haveli	First State/UT to achieve 100% FHTC
Paani Samiti	Village-level water committee for planning and maintenance
JJM Urban	Launched 2021 — tap water to every urban household

Other Important Water-Related Schemes

Scheme	Year	Key Feature
Namami Gange Programme	2014	Ganga rejuvenation; Rs. 20,000 crore; under NMCG (National Mission for Clean Ganga)
Atal Bhujal Yojana	2019	Groundwater management in 7 states
Swachh Bharat Mission (Water component)	2014	Solid/liquid waste management
National Water Policy	2012 (latest)	Guidelines for water resource management
National Water Mission	2011	Under NAPCC; 20% water-use efficiency improvement
Jal Shakti Abhiyan	2019	Water conservation in water-stressed districts

9. Water Quality Standards (CPCB)

Parameter	Drinking Water Standard (IS 10500)
pH	6.5-8.5
Total Dissolved Solids (TDS)	Max 500 mg/L (acceptable); 2,000 mg/L (permissible)
Turbidity	1 NTU (acceptable); 5 NTU (permissible)
Fluoride	Max 1.0 mg/L (acceptable); 1.5 mg/L (permissible)
Arsenic	Max 0.01 mg/L
Iron	Max 0.3 mg/L
Nitrate	Max 45 mg/L
E. coli/coliform	NIL per 100 mL

10. Previous Year PSC-Style Questions

Question	Answer
BOD stands for?	Biochemical Oxygen Demand
Higher BOD indicates?	More polluted water
Eutrophication is caused by excess of?	Nitrogen and phosphorus (nutrients)
Minamata disease is caused by?	Mercury poisoning
Itai-itai disease is caused by?	Cadmium poisoning
Jal Jeevan Mission was launched in?	2019
JJM target is?	Tap water to every rural household
Water Act was passed in?	1974
CPCB stands for?	Central Pollution Control Board
Chlorination is used for?	Disinfection (killing pathogens) in water
Blue Baby Syndrome is caused by?	Excess nitrate in water
Fluorosis is caused by?	Excess fluoride in water
Namami Gange Programme was launched in?	2014