Sources of Water Pollution (Cambridge International IGCSE Environmental Management)

Sources of water pollution

• Water pollution occurs when harmful substances enter rivers, lakes, groundwater or oceans
• This makes water unsafe for drinking, farming, fishing or wildlife
• Pollution can come from homes, farms, factories and improper waste disposal
• Understanding the main sources helps explain how water quality becomes degraded

Domestic waste

• Homes can produce many pollutants that enter drains and rivers

Soaps, detergents and cleaning products

• Contain chemicals that reduce water quality

  • Toxic chemicals from these types of products can kill fish or contaminate drinking water

Cooking oils and fats

• Oils washed down sinks form greasy layers on water surfaces and can clog drainage systems

Household rubbish and litter

• Items like wrappers, tissues or packaging can be carried into drains

  • These can block waterways and harm aquatic wildlife

Medicines and personal care products

• Medicines, shampoos or cosmetics flushed down drains introduce chemicals and hormones

  • Some of these substances can affect fish health and reproduction

Paints, oils and solvents

• Improper disposal through sinks or drains introduces toxic substances

  • These can poison aquatic organisms and contaminate water supplies

A polluted stream heavily littered with domestic waste

khyk54, CC BY 2.0, via Wikimedia Commons

Sewage

• Sewage contains harmful microorganisms and organic waste

• Untreated sewage entering rivers spreads disease-causing bacteria and viruses

  • This can lead to outbreaks of diseases such as cholera if people use the water for washing or drinking.

• Organic waste increases biological oxygen demand (BOD)

  • Biological oxygen demand is a measure of how much oxygen microorganisms need to break down organic waste in water
  • When lots of sewage or organic matter enter a river, bacteria use more oxygen to decompose it
  • High BOD means oxygen levels drop, leaving less oxygen for fish and other aquatic life
  • Low oxygen can cause fish to suffocate

Plastic waste

• Plastic bags, bottles and packaging enter rivers and oceans

  • These take hundreds of years to break down

• Wildlife may mistake plastic for food

  • This can block the digestive system and cause death

• Microplastics form when plastics break into tiny pieces

  • These can be ingested by aquatic organisms and enter the food chain

Industrial processes

• Factories may release chemicals, heavy metals and hot water

  • Toxic heavy metals, such as mercury or lead, can poison aquatic life
  • Warm water from industrial cooling systems causes thermal pollution
  • Warmer water holds less oxygen, stressing fish

• Industrial spills or leaks can contaminate large areas quickly

Agricultural practices

• Fertiliser run-off contains nitrates and phosphates

  • This causes algae growth and can lead to eutrophication

• Pesticides wash off fields and contaminate water

  • This can poison aquatic insects, fish and other wildlife

• Animal waste from farms can wash into rivers

  • Increases bacteria levels and reduces water quality

Exam Hint Students sometimes mix up domestic waste and sewage. Remember: domestic waste includes everyday household rubbish and wastewater (containing soaps, oils, detergents, etc.), while sewage specifically contains human waste and harmful pathogens from toilets and drains.