What is turbidity?

Turbidity is the cloudiness of water that is caused by suspended particles in the water, which are usually invisible to the naked eye. These particles could be soils, organic matter and microscopic organisms in the water, that range in size from 10nm in diameter to 0.1mm. Turbidity can enter a water supply system from land surface erosion and runoff from storm events or spring freshet.

Turbidity is measured in nephelometric turbidity units (NTU) (i.e. cloudy water has higher NTU values). It is not a direct measure of suspended particles in water but a measure of the scattering effect such particles have on light.  Since several factors affect the intensity of light scattering, turbidity measurements are not directly related to the number of suspended solids or particle counts.  


How does turbidity affect drinking water?

Turbidity can interfere with disinfection processes that are used in water treatment, such a ultra-violet radiation and chlorination. Turbidity can also significantly affect the microbiological quality of drinking water, because waterborne microorganisms, including some that may cause diseases in humans, can attach themselves to the suspended particles.

An increase in turbidity may increase the risk of gastroenteritis, especially for people with immunocompromised conditions. Health Canada recommends that all water used for infants under the age of four months should be boiled for two minutes.


How is drinking water treated to avoid turbidity?

Turbidity is treated by filtration and/or clarification/settling. Therefore, while turbidity is primarily an issue in unfiltered water systems, it can also indicate a problem with filtration.

Unfiltered surface water supplies can have variable levels of turbidity. There are times when the levels are low enough that no action is required, and times when higher levels of turbidity will interfere with proper treatment of the water and warrant a response from the water system operator.


What are the challenges in dealing with turbidity?

Determining when action is required depends on many factors, such as:

  • Level of the turbidity
  • Source of the turbidity
  • Whether the turbidity is increasing or decreasing
  • And many more!

What are the solutions to these challenges?

Depending on the specific situation, there are certain things that can be done. In some cases, more than one course of action might be followed. Some solutions might be to:     

  • Collect water samples more frequently
  • Increase turbidity monitoring
  • Increase the amount of chlorine being used for disinfection
  • Issue a water quality advisory or a boil water notice to the affected community

Who determines what solutions to follow when dealing with turbidity?

The water system operator often discusses the appropriate solution with their Environmental Health Officer who may also consult with the Drinking Water Leader or the Medical Health Officer.


What does all this mean for the general public?

If your public water supply has increased turbidity and there are health concerns associated with the turbidity, the operator, along with public health officials, will determine the next best steps, such as notifying the public if they need to boil their water to ensure it is safe for drinking.

Deep well systems sometimes experience increased levels of discolouration during flushing programs or because of components such as iron and manganese. These events are not generally associated with health concerns.


Where can I find more information?

If you would like more information on turbidity or a copy of the Northern Health turbidity guidelines, please contact your local environmental health office and ask for an Environmental Health Officer.