Water Pollution: Definition, Sources, and Remediation

Definition of Water Pollution

Water pollution refers to the degradation of water quality due to physical, chemical, and biological contaminants. This deterioration is caused by industrial, agricultural, and domestic activities, making water unsafe for consumption, irrigation, and aquatic life.

Water is often called the universal solvent, as it dissolves various substances, including detergents, pesticides, industrial chemicals, and effluents. However, when water accumulates waste materials and pollutants, it becomes contaminated and poses severe environmental and health hazards.

Sources of Water Pollution

Water pollution originates from various natural and human-induced activities. The major sources include:

1. Domestic Effluents and Sewage Household waste, including detergents, soaps, and personal care products, enters rivers, lakes, and groundwater. Improper sewage disposal leads to bacterial and viral contamination.
2. Industrial Effluents Factories discharge toxic chemicals, heavy metals (e.g., lead, mercury, cadmium), and synthetic dyes into water bodies. Chemical manufacturing plants, tanneries, and textile industries release highly hazardous waste.
3. Agricultural Effluents Excessive use of fertilizers, pesticides, and herbicides leads to runoff into water bodies, causing eutrophication (excess nutrient accumulation, leading to algal blooms). Animal waste from farms increases biological oxygen demand (BOD) and pathogen levels in water.
4. Radioactive Wastes Improper disposal of radioactive materials from nuclear power plants, hospitals, and research facilities contaminates groundwater and surface water.
5. Thermal Pollution Industries release hot water into lakes and rivers, altering the oxygen balance and aquatic ecosystems. Power plants and factories using water for cooling discharge heated wastewater, affecting fish and other organisms.
6. Oil Pollution Accidental oil spills from ships, tankers, and refineries cause severe water contamination. Oil films on water surfaces prevent oxygen penetration, harming aquatic life.

Causes of Water Pollution

1. Industrial Waste Factories release toxic chemicals, acids, heavy metals, and solvents into nearby water sources. Lack of proper wastewater treatment leads to contamination.
2. Sewage and Wastewater Urbanization and improper sewage disposal introduce disease-causing bacteria, viruses, and parasites into water. Untreated sewage can cause waterborne diseases like cholera, typhoid, and dysentery.
3. Mining Activities Mining exposes sulfide minerals, leading to acid mine drainage that contaminates rivers and groundwater. Heavy metals like arsenic, mercury, and lead leach into water bodies.
4. Marine Dumping Plastics, medical waste, and untreated garbage dumped into oceans disrupt marine ecosystems. Microplastics accumulate in aquatic food chains, posing health risks.
5. Accidental Oil Leaks Oil spills from ships, drilling rigs, and pipelines create long-term ecological damage. Oil coats marine life, suffocating fish and poisoning seabirds.
6. Burning of Fossil Fuels Combustion releases sulfur dioxide (SO₂) and nitrogen oxides (NOₓ), causing acid rain that contaminates water. Acid rain lowers the pH of lakes and rivers, harming aquatic organisms.
7. Chemical Fertilizers and Pesticides Excess fertilizers increase nitrate levels in water, causing blue baby syndrome (methemoglobinemia) in infants. Pesticides like DDT and organophosphates accumulate in water and enter the food chain, leading to toxicity.

Remedial Measures to Control Water Pollution

1. Municipal Wastewater Treatment Primary, secondary, and tertiary treatments remove pollutants before releasing water into natural sources. Sewage treatment plants (STPs) reduce organic waste and pathogen load.
2. On-Site and Safely Managed Sanitation Properly designed septic tanks and bio-toilets minimize water contamination. Rainwater harvesting reduces surface runoff and groundwater depletion.
3. Industrial Wastewater Treatment Effluent Treatment Plants (ETPs) remove toxic chemicals before discharge. Industries should adopt zero-liquid discharge (ZLD) techniques to recycle water.
4. Agricultural Waste Management Use bio-fertilizers and organic manure instead of synthetic fertilizers. Implement integrated pest management (IPM) to minimize pesticide usage.
5. Erosion and Sediment Control from Construction Sites Proper drainage, silt fences, and vegetation cover prevent soil erosion into water bodies. Green infrastructure solutions like wetlands and rain gardens filter runoff.
6. Control of Urban Runoff Stormwater management systems like infiltration basins and pervious pavements reduce runoff. Proper waste segregation prevents plastic and chemical pollution in urban water bodies

Characteristics that Determine Quality of Irrigation Water

1. Total Concentration of Soluble Salts (EC): Determines water salinity and potential for soil salinization.
2. Relative Proportion of Sodium to Other Cations (SAR): Influences soil permeability and structure.
3. Concentration of Boron or Other Toxic Elements: High levels can be toxic to crops.
4. Bicarbonates Concentration Relative to Calcium and Magnesium: Affects soil alkalinity and water suitability.

Criteria and Standards for Assessing Suitability of Saline Water for Irrigation

Irrigation water suitability is based on its potential impact on soil conditions and crop growth:

• Permeability and Tilth: High sodium and pH levels can degrade soil structure, causing crusting and poor infiltration.
• Salinity: High salt concentration reduces plant transpiration, leading to stunted growth.
• Toxicity and Nutritional Imbalance: Elements like chloride, sodium, and boron can cause leaf burn and defoliation.

Classification of Irrigation Water

1. Based on Salinity Hazard

2. Based on Sodium (Alkali) Hazard (SAR)

SAR = Na⁺ / (Ca²⁺ + Mg²⁺)/2

3. Based on Residual Sodium Carbonate (RSC)

RSC = (CO₃²⁻ + HCO₃⁻) – (Ca²⁺ + Mg²⁺)

4. Concentration of Boron

Tolerance of Plants to Boron

• Tolerant: Sugar beet, onion, turnip, cabbage, lettuce.
• Semi-Tolerant: Sunflower, potato, tomato, radish, wheat.
• Sensitive: Apple, grape, fig, cherry, apricot, orange.

Utilization of Saline and Sewage Water in Agriculture

Management Practices for Safe Use of Saline Water

1. Crop Selection: Choose salt-tolerant varieties.
2. Special Planting Procedures: Reduce salt accumulation near seeds.
3. Irrigation Management: Maintain high soil moisture and periodic leaching.
4. Land Preparation: Improve water distribution and salt removal.
5. Soil Amendments: Use organic matter, green manure, and chemical treatments to improve soil condition.

Managing Soils Under Saline Water Irrigation

Tillage

• Enhances seedbed preparation and improves permeability.
• Avoid excessive machinery use to prevent compaction.

Deep Ploughing Breaks compact layers, improves water retention, and enhances drainage.

Sanding Mixing sand with fine soil increases permeability and reduces water stagnation.

Chemical Amendments

• Gypsum: Most effective for sodic soil reclamation.
• Calcium Chloride: Highly soluble and improves soil structure.
• Sulfur and Sulfuric Acid: Reduce soil pH and promote calcium availability.

Organic and Green Manures Improve soil permeability and fertility. Reduce exchangeable sodium and enhance crop growth.

Mulching Reduces evaporation, prevents salt accumulation, and enhances soil structure.