Water Quality: Microbiological Contamination

All water sources contain naturally occurring bacteria, the majority of which are harmless to humans and easily removed through traditional disinfection methods.

Surface waters such as lakes, reservoirs, rivers and streams are more susceptible to microbiological contamination and are likely to demonstrate seasonal variation with numbers increasing after periods of rainfall or alteration to the local land use.

The presence of certain micro-organisms can give a good indication of the quality of a water. These include the group of organisms termed coliforms.

Coliforms indicate fecal contamination of the water source, typically from animals grazing in the catchment area. If there is a high number of these organisms it indicates that the water supply has been contaminated. The risk of infection from these organisms is easily removed by the traditional disinfection processes of chlorination and ultra violet disinfection.

Of greater concern, although a rare occurrence, is contamination of a water source with either Cryptosporidium or Giardia organisms.

Both of these organisms create protective oocysts which are resistant to traditional disinfection processes.

Cryptosporidium is unaffected by chlorination and other traditional methods, and can only be effectively removed by micro-filtration or other more advanced techniques

Giardia is also resistant to traditional treatment and again micro-filtration is required to physically remove this organism.