Water Quality

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Survey types of water pollution

(note: for discussion of water quantity and supply see the previous section)


Safe drinking water and sanitation are two of the most important indicators of quality of life. They make up Goal 6 of the Sustainable Development Goals.

  • Water scarcity affects 40% of the world's population.
  • 1.8 billion people use a contanimated drinking water source.
  • About one-third of the World's population (2.4 billion) have improper sanitation.
  • 80% of all wastewater is discharged without treatment.
  • Every day, 1000 children die of diarrheal diseases

Diseases related to contamination of drinking-water constitute a major burden on human health. Interventions to improve the quality of drinking-water provide significant benefits to health.

World Health Organization

Point versus Nonpoint

Two types of water pollution sources:

  • Point sources: pollution is from a specific location
Examples: pipe, sewer, oil well
  • Nonpoint sources: not from any single site
Examples: agricultural runoff, oil from city streets
Nonpoint sources are very difficult to control
A point source
River polluted by sediment, a typical nonpoint source


Types of water pollution

  • pathogen
  • dissolved organic matter
  • nutrients
  • sediments
  • heat
  • toxic chemicals


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Bacteria, viruses, and parasites which can cause disease

The source of pathogens in water is human and animal wastes. Since here we are talking about waterborne diseases, if they are found in water they must originate from the gut of either animals or humans.

Vibrio cholerae, the bacteria that causes cholera

They can cause some very serious diseases, such as amoebic dysentary, typhoid, polio, and cholera.


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E. coli and related bacteria

Coliforms are only naturally found in the gut of animals (including humans). Therefore, we can use the concentration of coliform in water as an indicator of possible presence of pathogens. The coliform test is a very commonly used test for water pollution.

Dissolved Oxygen

Dissolved Oxygen - Oxygen which is dissolved in the water

It is necessary for fish and other aquatic organisms to survive. Often it is the limiting factor for these species.

Dissolved Organic Matter


Dissolved Organic Matter includes manure and plant debris. Human sources include sewage, runoff from feedlots, and paper mills.

A major fish kill in Brazil


  1. Microorganisms (decomposers) breakdown the dissolved organic matter
  2. As these decomposers use oxygen, they remove dissolved oxygen from the water.
  3. The resulting lowered dissolved oxygen my be too low for fish to survve, causing fish kills.


The measure of the amount of oxygen-demanding wastes is the Biological Oxygen Demand (BOD). It is the amount of dissolved oxygen needed by aerobic decomposers to break down organic matter at 20 degrees Celsius in 5 days.


Ironically, nutrients - especially nitrates and phosphates - can cause water pollution.

Sources: sewage, agricultural runoff from fertilizers, detergents (these contain phosphorus).

Excess nutrients can cause a condition called eutrophication.

An algae bloom in a pond in N. Carolina, USA


  1. Excess nutrients cause algae and other aquatic plants to grow (an algal bloom)
  2. When these die, decomposers feed on them deplete the dissolved oxygen
  3. This can kill fish and other aquatic organisms.


Fine particles can become suspended in the water column. The main source is soil erosion.

Rhone river flowing into Lake Geneva, notice the brownish-grey sediment flowing out of the river

They can have a number of effects:

  • reduce photosynthesis
  • carry bacteria, toxic chemicals, and nutrients
  • settle on the bottom covering fauna
  • fill lakes and reservoirs

Thermal pollution

Water used to cool power plants and other industries is often released to rivers or lakes.

Outflow of water from the Potrero Power Plant. This is thermal pollution

This hot water changes the water temperature. This in turn lowers dissolved oxygen and disrupts the normal activity of aquatic organisms.

It also increases evaporation.

Toxic chemicals

Many chemicals are toxic: lead, arsenic, pesticides, oil, etc.

Sources: surface runoff, industrial effluents, seepage from landfills.

Toxic chemicals can cause a variety of health effects. They can also harm fish and wildlife.

Wastewater Treatment

Wastewater treatment is the removing of contaminatess found in wastewater. This section will focus on municpal wastewater (sewage). Note: do not confuse wastewater treatment with water treatment.


Let us look at the above components individually:

  • Filter - this is to remove large pieces of debris such as bottles, wood, or metal
  • Settling Tank - removes non-organic materials - for example, soil
  • Aerobic Decomposition - most commonly Activated Sludge system which pumps air into the wastewater to encourage bacterial decomposers to digest the waste.
  • Anaerobic Digestion - decomposes any remaining organic matter in the sludge

Some other parts may also exist:

  • In place of an activated sludge system, trickling filters may be used. These slowly run water of rocks onto which bacteria to form a film.
  • For small-scale uses, a septic tank - these tanks act as both a settling tank and as a place for degradation of organic waste
  • Wetlands may be used after the primary treatment. This uses the natural process to treat the waste.


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Investigate what drinking water source is used in your home town. Be as specific as possible. What, if any, treatment is done to this water before it reaches your home?

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Read the following articles:

Sanitation Too Often Overlooked in Developing Nations
Nano Tea Bags
Lake Erie

Then answer the following questions:

  1. What role does local government play in sanitation?
  2. In addition to the use of nanofibres in the article, in what other ways can they be used to clean water?
  3. What measures could be done to reduce the sediment and nutrient loads on Lake Erie?
  4. Would any of the solutions mentioned in the articles apply to non-point sources?
  5. The Theme of the 2010 World Water Week is ""The Water Quality Challenge - Prevention, Wise Use and Abatement". List what topics would you include if you could write the agenda for this seminar?