Water pollution occurs when harmful substances—chemicals, microorganisms, or industrial waste—contaminate a stream, river, lake, ocean, or aquifer, degrading water quality and rendering it toxic to humans or the environment. In India, water pollution is a critical challenge linked to rapid urbanization and unregulated industrial discharge.
Classification of Water Pollutants
Pollutants are broadly classified into three categories based on their nature.
- Biological Pollutants: Pathogens such as bacteria (E. coli), viruses, and protozoa that enter water through untreated domestic sewage.
- Chemical Pollutants: Heavy metals (Lead, Mercury, Arsenic), nitrates from fertilizers, and persistent organic pollutants (POPs) from pesticides.
- Physical Pollutants: Thermal discharge (heat) from power plants and suspended solids (silt) from construction or deforestation.
Primary Sources of Water Pollution
| Source Category | Key Pollutants | Impact |
| Domestic Sewage | Organic waste, detergents, pathogens. | Leading cause of water-borne diseases and high BOD. |
| Industrial Effluents | Heavy metals, toxic chemicals, acids. | Bioaccumulation in the food chain; toxic to aquatic life. |
| Agricultural Runoff | Nitrates, phosphates, pesticides. | Causes Eutrophication and Algal Blooms. |
| Oil Spills | Petroleum hydrocarbons. | Smothers marine life and disrupts oxygen exchange. |
Key Indicators of Water Quality
To assess the level of pollution, scientists use specific biochemical parameters.
Biological Oxygen Demand (BOD)
BOD is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample.
- High BOD: Indicates high levels of organic pollution (sewage).
- Low BOD: Indicates clean water with low organic waste.
Chemical Oxygen Demand (COD)
COD measures the oxygen required to chemically oxidize all organic and inorganic matter in water. It is generally higher than BOD and provides a faster assessment of pollution.
Dissolved Oxygen (DO)
The amount of free oxygen available in water. A DO level below 4 mg/L is considered heavily polluted and lethal to most fish.
Eutrophication and Algal Blooms
Eutrophication is the process by which a body of water becomes overly enriched with minerals and nutrients (specifically Nitrogen and Phosphorus).
- Mechanism: Nutrient enrichment leads to the rapid growth of algae (Algal Bloom).
- Impact: The thick layer of algae prevents sunlight from reaching submerged plants. When the algae die, bacteria consume nearly all the DO to decompose them, creating “Dead Zones” where no aquatic life can survive.
Heavy Metal Contamination in India
Specific regions in India face localized health crises due to geological and industrial groundwater contamination.
- Arsenic: Found in the Ganga-Brahmaputra plain (West Bengal, Bihar). Causes Blackfoot Disease and skin lesions.
- Fluoride: High levels in Rajasthan and Telangana. Leads to Fluorosis (skeletal and dental deformities).
- Mercury: Often from industrial discharge. Causes Minamata Disease (neurological damage).
- Cadmium: Causes Itai-Itai Disease, characterized by painful bone softening.
Legislative and Institutional Framework
The Water (Prevention and Control of Pollution) Act, 1974
This is the primary legislation for water quality management in India. It led to the establishment of the Central Pollution Control Board (CPCB) and State Pollution Control Boards (SPCBs).
Namami Gange Programme
An Integrated Conservation Mission launched in 2014 to accomplish the twin objectives of effective abatement of pollution and conservation of the National River Ganga.
- Main Pillars: Sewage treatment infrastructure, river-front development, river-surface cleaning, and bio-diversity conservation.
Remediation Technologies
- Phytoremediation: Using green plants to remove, transfer, or stabilize pollutants in water (e.g., Water Hyacinth for heavy metals).
- Bioremediation: Using microbes to break down contaminants like oil spills (e.g., Oil Zapper developed by TERI).
- Reverse Osmosis (RO): A membrane-based process used to remove dissolved solids and ions.
Trivia and Facts for UPSC
- Biomagnification: The process where the concentration of a toxin (like DDT or Mercury) increases as it moves up the food chain.
- Point vs. Non-Point Source: A “Point Source” is a single identifiable pipe or factory. A “Non-Point Source” is diffuse, like agricultural runoff or city-wide storm drainage.
- Benthic Zone: Pollution often settles at the bottom of water bodies, severely affecting benthic (bottom-dwelling) organisms which serve as early warning indicators.