Sources, effects and remedies of water pollution

Water pollution is the contamination of water bodies by substances that make water unfit for its use and harm living things.

Major sources

• Domestic sewage: human waste, kitchen waste, detergents.
• Industrial effluents: acids, alkalis, dyes, heavy metals (Pb, Hg, Cd, As, Cr), oils and phenols, from tanneries and from paper, textile, sugar and chemical industries.
• Agricultural runoff: fertilisers (nitrates, phosphates), pesticides (DDT) and animal wastes.
• Mining and oil: acid mine drainage, oil spills.
• Thermal pollution: hot water from power plants and industries.
• Others: radioactive wastes, landfill leachate, siltation from soil erosion, religious and cultural offerings, municipal solid waste dumping into rivers.

Adverse effects

• Health: waterborne diseases (cholera, typhoid, dysentery, hepatitis, diarrhoea); Hg causes Minamata disease, Cd causes itai-itai disease, As causes arsenicosis (found in groundwater of the Terai), Pb damages the brain; nitrate in water causes blue-baby syndrome.
• Eutrophication: excess nitrate and phosphate cause algal blooms; when the algae die, their decay uses up dissolved oxygen (high BOD, low DO) and fish die.
• Bioaccumulation and biomagnification of pesticides and metals in the food chain.
• Bad taste, smell and colour; water is unfit for drinking, irrigation and industry.
• Thermal pollution reduces oxygen solubility and disturbs aquatic life.

Possible remedies

• Treat sewage and industrial effluents before discharge (primary, secondary and tertiary treatment).
• Use less fertiliser and pesticide; use organic farming; ban phosphate detergents.
• Prevent dumping of solid waste in rivers; build proper sanitation and toilets.
• Cool hot water before discharge; recycle and reuse water.
• Strict laws (polluter pays), regular monitoring, public awareness and river-cleaning programmes (such as for the Bagmati).