Email This Print this page More...

Causes of Water Pollution

 languages This article is available in: English | Afrikaans | Sotho | Zulu

Causes of water pollution


Urbanisation causing water pollutionAs more and more people move into cities and towns, a number of factors cause pollution:

  • the physical disturbance of land due to construction of houses, industries, roads, etc.;
  • chemical pollution from industries, mines, etc.;
  • inadequate sewage collection and treatment;
  • increase in fertilisers to grow more food. This results in an increase in nutrients (nitrates and phosphates) in the water which causes enhanced plant growth (algal blooms). When this plant material dies and decays the bacteria uses the oxygen in the water. This lowering of oxygen levels results in the death of other water life that needs oxygen to survive, eg. fish, etc. This process is called eutrophication;
  • litter, which causes disease and has a negative visual impact.


Clearing land for agriculture and urban growth often leads to water pollution. When soil is stripped of its protective vegetation it becomes prone to soil erosion. This leads to an increase in the murkiness of the water which can cause the following:

  • it can block the gills of fish;
  • bottom dwelling plants cannot photosynthesize as the sun’s rays cannot reach them; and
  • there is an increase in disease as bacteria and viruses use the soil particles as a method of transportation.

Polluted River                            Vaal Dam

Polluted river and vaal dam

Damming of Rivers

Damming of rivers can have an impact on water in the following ways:

  • Water flowing out of dams:
    • has reduced suspended material as a large amount settles to the bottom of dams;
    • is depleted of nutrients; and
    • is often more saline
  • with detrimental effects on downstream agriculture and fisheries.
  • Enhanced eutrophication may result due to the water spending a longer time in the dam.
  • There is also increased evaporation in dams, especially those with a large surface area, such as the Vaal Dam.

Destruction of Wetlands

Wetlands in South AfricaWetlands are nature’s way of cleaning water as well as damming water (they hold back water in summer and release it in winter).
Destruction of wetlands:

  • Destroys the habitat of many birds and fish;
  • Removes the natural filters capable of storing and degrading many pollutants, such as phosphorus and heavy metals;
  • Destroys natural dams and causes flooding further downstream.


Industry causing pollutionIndustries produce waste that can affect the:

  • pH of water (whether it is acid, neutral or alkaline);
  • colour of water;
  • amount of nutrients (increase in nutrients can cause eutrophication);
  • temperature (increase or decrease in temperature can have an impact on temperature sensitive organisms living in the water);
  • amount minerals and salts (too much can cause health problems);
  • murkiness of water (can block fish gills; bottom dwelling plants cannot photosynthesize as the sun’s rays cannot reach them; increase in disease as bacteria and viruses use the soil particles as a method of transportation).


Mining causing pollutionMines produce waste that:

  • can increase the amount of minerals and salts in the water (too much can cause health problems);
  • can affect the pH of the water (whether it is acid, neutral or alkaline);
  • can increase the murkiness of the water.


  • AgricultureIncreases soil erosion due to the physical disturbance of soil and vegetation due to ploughing, overgrazing, logging and road building. This effects the murkiness and the amount of salts and minerals in water;
  • Increases nutrients due to fertilisers and excreta, which contribute worrying amounts of nitrates and phosphates to water supplies (this can cause eutrophication);
  • Increased pesticide use.

Energy Use

Energy use in South Africa

As human populations increase, more energy is required for human activities such as cooking, lighting, etc. The majority of our energy in South Africa comes from the burning of coal at power stations and results in greatly increased emissions of sulphur and nitrogen oxides into the atmosphere. These gases are the main cause of acid rain. Also the release of carbon dioxide, from the burning of coal, increases global warming.

Accidental Water Pollution

Accidental water polllution

Accidental water pollution can arise from many sources (such as burst pipes and tanks, major leaks, fires and oil spills) and can cause varying degrees of damage, depending on the quantity, toxicity and persistence of the pollutant, and the size and adaptability of the water body.

The Future

If this is the water situation at present, what of the future? South Africa can build more dams and water transfer schemes; desalinate sea water; source water from neighbouring countries, such as the Zambezi River in Zimbabwe; reusing effluent water; or treating mine wastewater. But all of these solutions are expensive and not affordable for the country. In terms of water quality, South Africans can clean up rivers and impose fines on those people/companies that pollute rivers. But these solutions address the symptoms of the problem. We should be addressing the cause of the problem, i.e. our attitude towards water.

The future of South Africa lies in our hands. We can make a difference. We just need to understand the water environment and how we humans fit into it. We all need to become “Water Wise”! But what does it mean to be “Water Wise”?

To be “Water Wise” means that a person will:

  • have the utmost RESPECT for water and all life;
  • use water carefully and not WASTE it;
  • not POLLUTE rivers with liquid and solid waste;
  • PAY for water services;
  • take ACTION to solve any water problems;
  • CONSERVE water, and thereby CONSERVE the natural environment.

South Africa has, in general, a limited supply of water and the quality of this water is being threatened by pollution and the destruction of river catchments. Water is a vital resource and it is up to ALL South Africans to act responsibly in their daily lives and look after the available water resources to ensure that this limited supply is usable by all life on earth. It is very important that everyone becomes “Water Wise”.

See also

What does it mean to be Wise Wise?
Are you Water Wise? Take our Quiz
The Water Wise Song