Water pollution: sources, causes and impacts

Water pollution is any physical, chemical or biological change in the quality of water that makes it harmful to people and living organisms or unfit for its intended use (drinking, irrigation, industry, recreation).

Major sources

• Point sources – come from one identifiable place: sewage outfalls, industrial effluent pipes, hospital waste water.
• Non-point sources – spread over a large area: runoff from farms, urban streets, landfills and open defecation areas.

Causes

1. Domestic sewage discharged untreated into rivers (e.g. Bagmati in Kathmandu).
2. Industrial effluent – tanneries, dyeing, distilleries, paper mills release chemicals and heavy metals.
3. Agricultural runoff – fertilisers (nitrate, phosphate) and pesticides.
4. Solid waste dumping on river banks.
5. Open defecation and leaking septic tanks contaminating groundwater.
6. Natural sources – arsenic, iron and manganese in groundwater (Terai), sediments from landslides.
7. Oil spills, mining and sand extraction.
8. Thermal pollution – hot water from industries.

Impacts

• Health – water-borne diseases: cholera, typhoid, diarrhoea, hepatitis; arsenicosis from arsenic; blue-baby syndrome from nitrate.
• Aquatic ecosystem – organic matter consumes dissolved oxygen, fish die; eutrophication (algal bloom) from nutrients.
• Biomagnification of toxic substances (mercury, DDT) along the food chain.
• Economic – higher water treatment cost, loss of fisheries and tourism.
• Agriculture – polluted irrigation water harms crops and soil.
• Social and cultural – holy rivers and ghats lose their value; foul smell and nuisance in cities.

Control: sewage treatment, effluent standards for industries, safe sanitation, controlled use of agro-chemicals and protection of water sources.