Water Microbiology


Drinking Water Testing


Total Coliform (Bacteria) Testing

Total coliforms are indicator organisms used to detect bacterial contamination in drinking water. Their presence indicates that a pathway for contamination exists and organisms that cause disease may be present, even though total coliforms themselves typically do not cause disease in healthy individuals. The most common symptoms caused by disease-causing organisms in drinking water are nausea, vomiting and diarrhea.

Total coliforms are found naturally in soil, surface water, plant material, and insects; however, one species of total coliform (E. coli) is found in the feces of warm blooded animals. Total coliforms are not naturally found in well water or groundwater. Wells should be tested yearly if there is a history of total-coliform-absent (bacteriologically safe) results, or more frequently if there is a change in the water quality because of color, taste or odor.


E. coli Testing

E. coli is an indicator organism of fecal contamination. The natural habitat for E. coli is the intestinal tract of warm-blooded animals. The presence of E.coli in a drinking water sample is an indication of fecal contamination of the water supply. E. coli is a subset of total coliform, so if there is no total coliform present in the water sample, there is no E. coli.


Iron Bacteria

Iron bacteria are naturally present in surface water and soil. Iron bacteria do not cause illness but are considered nuisance bacteria. They can produce orange/brown slime that builds up inside well screens, pipes and plumbing fixtures. The presence of odors and/or brown-tinted water and/or brown-tinted staining on fixtures is an indication of iron bacteria. The treatment for iron bacteria is disinfecting the well.


Sulfate Reducing Bacteria

Like iron bacteria, sulfate reducing bacteria do not cause illness, but are nuisance bacteria. They are found in soil and surface water. Sulfate reducing bacteria can lead to corrosion in well casings, pipes, cement and other materials and can produce an unpleasant odor (rotten egg) in water. The treatment for sulfate reducing bacteria is disinfecting the well.


Heterotrophic Plate Count

This test estimates the number of live bacteria that are able to grow on a specific media at a specific temperature and incubation period. This test measures changes during water treatment and in a distribution system. This test is also one of several used to measure the disinfection efficiency of whirlpools, pools and spas.


Recreational Water Testing


Swimming Beach Testing

Swimming beaches should be tested for water quality before the swimming season begins—to get a baseline of contamination resulting from natural wildlife or run-off—and each week thereafter until the season ends. Beaches may be regulated by local ordinances or local health standards. The standards developed for the Great Lakes in Wisconsin and may be used for inland beaches are:

  • If the E. coli count is greater than 1000 MPN/100 mL, the beach is closed.
  • If the E. coli count is greater than 235 MPN/100 mL but less than 1000 MPN/100 mL, an advisory is issued.
  • If the E. coli count is under 235 MPN/100 mL, the beach has no advisories or warnings issued.


Total Coliform (Swimming Pool) Testing

This test is one of several used to measure the disinfection efficiency of swimming pools and whirlpools.


Pseudomonas aeruginosa

Pseudomonas aeruginosa is considered an opportunistic pathogen and may cause skin rashes when appropriate levels of disinfection are not maintained in whirlpools and pools. This test is one of several used to measure the disinfection efficiency in whirlpools, pools and spas.


Surface Water Testing

Various tests are used to investigate recreational water, stream or lake pollution, and wastewater treatment systems. The following are tests available for surface water testing:

  • E. coli: The only natural habitat of E. coli is the intestinal tract of warm-blooded animals.
    • The recreational water guideline is less than 126 MPN/100 ml, averaged from 5 samples during a 30-day period.
    • The single sample guideline is less than 235 MPN/100 mL.
    • An advisory is recommended between and 235 MPN/100 mL and 1000 MPN/100 mL.
    • A closure is recommended at greater than 1000 MPN/100 mL.
  • Enterococci: This refers to a subgroup of the fecal enterococci that includes Enterococcus faecalis, Enterococcus faecium, Enterococcus gallinarum and Enterococcus avium. The enterococci are used to indicate water quality.
    • The recreational water guideline is 33 MPN/100 ml, averaged from 5 samples during a 30-day period.
    • The single sample guideline is less than 61 MPN/100 mL.


Beach Water Collection for E. coli Testing (video)

Using the appropriate sampling protocol to collect beach water samples for E. coli testing is critical to effectively protect the health of public beach users. This 12-minute video provides instructions on how to properly collect beach water samples for E. coli testing. Public health sanitarians, resort owners and anyone required to test swimming beaches for E. coli will find this video a valuable resource. (Windows Media Player is required for viewing.)

High-bandwidth video (2 Mbps)

Low-bandwidth video (81 Kbps)

The video was funded and produced by the Wisconsin State Laboratory of Hygiene, with additional funding provided by the Wisconsin Department of Natural Resources and the Wisconsin Department of Health Services.


Microbial Source Tracking


Bacteroides spp.

Bacteroides spp. is present in human and animal fecal material. They are strict anaerobes so they do not grow in the environment. The presence of Bacteroides spp. indicates fecal contamination. A series of DNA-based tests can be used to determine whether fecal contamination is present in a source water (surface or well water), and whether that contamination may be of human or bovine (cow) origin.


Sorbitol-fermenting Bifidobacteria

Sorbitol-ferementing Bifidobacteria are present in human fecal material. They are strict anaerobes, so they do not grow in the environment, making them excellent indicators of recent human fecal contamination.


Rhodococcus coprophilus

Rhodococcus coprophilis is found in association with manure of domesticated grazing animals like cows, sheep, horses, goats, etc. To date it has never been isolated from human feces. The presence of Rhodococcus coprophilis indicates grazing animal contamination.


Male-specific coliphage genotypes

Male-specific coliphages are viruses that infect coliforms. As such, their presence indicates the presence of fecal contamination in a water source. These viruses can be enumerated and genotyped. Group I and IV coliphages are associated with non-human fecal sources, while Group II and III are associated with human fecal sources.