Water Treatment Basics – Contaminants

3. Common Water Contaminants

Microbiological Contaminants

Microbe Type Example Disease Examples Approx Size
VIRUSES Hepatitis, Coronavirus, Poliovirus Hepatitis A, SARS, Polio 0.005 Micron
BACTERIA E. coli, Salmonella, Shigella Diarrhea, Dysentery, Typhoid, Cholera 0.5 – 2.0 Micron
CYSTS Cryptosporidium, Giardia Beaver Fever 2 – 4 Micron
PARASITES Tapeworm, Ascaris GI Infection, Guinea Worm Disease 35 – 75 mm (eggs)



  • Lead does not occur naturally in water
  • Homes built before 1986 – lead service pipes, fixtures and lead-based solder.
  • Over time, water and chloramines corrode lead plumbing, causing traces of lead to leach into drinking water.
  • Higher levels of lead can cause delayed physical and mental development in children, spikes in blood pressure & increased risk of kidney problems


VOC (Volatile Organic Compounds)

  • Chemicals from fuels, solvents, polishes, cosmetics, dry cleaning solutions etc
  • Spilled on the ground or dumped in toilets, eventually carried to water sources.
  • Most VOCs are potential or known carcinogens


Trihalomethanes (THM)

  • TriHaloMethanes
  • A by-product formed when chlorine reacts with organic compunds
  • Chloroform is an example
  • Like VOC, THMs are also potential carcinogens



  • Turbidity is the degree of cloudiness of water
  • Sand, mud, fine silt, rust to minute microscopic particles, all contribute to turbidity
  • Do not usually have any direct health hazard, but can harbour pathogenic microorganisms
  • Degree of turbidity is measured in “Nephelometric Turbidity Units” or simply NTU
  • Drinking water should have turbidity less than 1.0 NTU



  • Most common problem in municipally treated water
  • Not considered a direct health risk
  • Many people are allergic to chlorine
  • Most don’t like the smell & taste
  • Affects taste of water and beverages


Hardness (Hard Water)

  • Very common problem in well waters with limestone/marble
  • Forms a whitish scale deposits
  • Hard water does not form lather easily
  • Hardness is measured in Grains Per Gallon (GPG) or PPM. (1 GPG = 17.1 PPM)



Iron stains on bath tub

  • Usually in well water. Present in the dissolved form as “Ferrous Iron”. Contact with air makes it into “Ferric Iron” (Rust).
  • Over 0.3 PPM (mg/L) iron causes reddish brown staining of plumbing fixtures, clothes, etc.
  • It also gives water an unpleasant metallic taste



  • Like Iron , it is found in ground water in the dissolved form until it comes into contact with air.
  • Causes black deposits on fixtures and clothing if present over 0.05 PPM (mg/L)
  • Health Canada has established an aesthetic objective of 0.02 PPM (mg/L)
  • If present in water, it will usually be accompanied by Iron.


Hydrogen Sulphide

  • Gives water a distinct offensive rotten egg odour, even in very low concentrations
  • Usually accompanies iron &/or manganese in well waters.
  • Tarnishes silver almost instantaneously



tannins in water

  • Tannins are organics that are produced by decomposition of vegetation.
  • Impart a faintly yellowish or brown colour to water.
  • They are not a direct health hazard but make the water aesthetically unpleasant and reduce performance of disinfection devices such as UV
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