Water Quality

Edexcel iGCSE > River Environments > Water Quality

Water Quality

Why are there variations in water quality?

Water quality differs globally due to various factors, including:

  • Agricultural run-off: Factory farming contributes significantly to water pollution, contaminating water sources with fertilizers, pesticides, and animal waste.
  • Industrial pollution: Industries often discharge pollutants into rivers and other water bodies, significantly degrading their quality.
  • Urban run-off: Urban areas contribute to water pollution through run-off that carries pollutants from cars, factories, and other sources.
  • Untreated sewage: Much wastewater is released into the environment without being collected or treated.

Each year, over 80% of the world’s wastewater is discharged untreated into the environment. This pollutes our surroundings and results in the wastage of a renewable resource. While affluent countries have seen improvements in water quality, rivers in many developing regions, particularly in Asia, have become more polluted.

The storage and supply of clean water

In regions like the Canadian province of Alberta, various water supply and management methods are used.

Wells and boreholes

These are dug straight down to the water table. Replenished by these wells and boreholes, aquifers provide approximately half of the world’s drinking water, 40% industrial water, and up to 30% irrigation water. For instance, 35% of all public water supply in England and Wales comes from groundwater, which is even more critical in arid and semi-arid regions.


Developed countries generally have more extensive water redistribution networks than developing ones, owing to the high cost of water infrastructure. However, water grids are not as widespread as power grids, limiting the ability to move water from surplus to deficit areas.

Water treatment

Almost all water sources need some degree of treatment to make them safe for human consumption due to contamination from human activities and natural sources.

  • Developed countries primarily use central source treatment systems. These involve physical processes like sedimentation, filtration, and disinfectant processes such as chlorination.
  • In developing countries, where central treatment systems may be non-existent or lacking capacity, point-of-use (POU) treatment is often employed.
  • Compared to surface water, groundwater tends to be relatively cleaner.

Losses in water transport systems are also a significant concern. Well-maintained urban water systems in developed countries lose between 10% and 30% of transported water. In contrast, this loss can be as high as 70% in developing world cities.


  • Water quality varies globally due to factors like agricultural run-off, industrial and urban pollution, and untreated sewage, with increased pollution in developing regions.

  • Wells and boreholes are used to access aquifers that provide significant amounts of global drinking, industrial, and irrigation water.

  • Water sources require treatment before consumption, with developed countries using central source systems and developing countries often resorting to point-of-use treatment.

  • Transfers include evaporation, transpiration, condensation, precipitation, overland flow, infiltration, percolation, throughflow and groundwater flow.

  • Significant water loss during transport is a common issue, with losses being notably higher in developing cities.


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