Fact sheet on coliform bacteria in drinking water

General
Coliform bacteria belong to the Enterobacteriaceae (enteric bacteria). They play an important role as an indicator parameter in drinking water testing. Coliform bacteria are an important indicator, especially for detecting hygiene deficiencies and usually non-fecal contamination.
The Drinking Water Regulation requires the absence of coliform bacteria (0 CFU/100 ml). If coliform bacteria are detected, appropriate countermeasures must be initiated immediately. A positive detection of coliform bacteria in a drinking water sample according to the Drinking Water Regulation must be reported to the competent authority.

Characteristics

• Rod-shaped bacteria
• Gram-negative
• Oxidase-negative
• Catalase-positive

Origin / Occurrence

• Widespread in our environment (e.g., soil, plants, surface water)
• Coliform bacteria are also natural intestinal inhabitants of animals and humans

Significance

• Hygiene indicator in drinking water testing: The occurrence of coliform organisms can indicate a disturbance in the drinking water cycle or the ingress of foreign matter into the distribution network.
• With a positive finding at a connection, the piping should be checked for damage, biofilm formation, backflow and/or inflow of non-potable water.

Important

• An introduction of coliform bacteria into the pipe system is also possible due to improper handling, repair or maintenance
• If coliform bacteria are detected, a longer series of samples from various sampling points is often required to obtain meaningful results. It may also be useful to collect 1000 ml samples.
• Among the coliform bacteria there may also be organisms that can be facultatively pathogenic for vulnerable groups. These include, for example, Klebsiella, Enterobacter, Citrobacter and E. coli

Growth conditions

• Temperature:
  • Optimum: generally at +30 °C to +37 °C
  • Minimum: usually +7 °C (depending on the species, exceptions even down to 0 °C)
  • Generally no growth above +50 °C
• pH value: growth at pH 5.5 to 9.0 (depending on the species, exceptions even down to pH 4.4)
• a_w value: growth at high water activity of at least 0.95
• Oxygen requirement: growth with and without oxygen (facultative anaerobe)

Inactivation by heating

• Exposure at +72 °C for at least 2 minutes will kill vegetative bacteria (Note: check core/internal temperature)

1. If an aerator/perlator is present: remove and disinfect. Replace depending on condition
2. Remove contamination and/or biofilms
3. If possible, flame the last section of the water outlet after cleaning
4. Verify success by follow-up testing

1. Possibly perform stepwise investigations to better identify the location of contamination in the distribution network
2. Engage a specialist company or building services to investigate the cause
3. Perform disinfection
4. Verify success by follow-up testing

1. Thorough visual inspection of the treatment system
2. Check maintenance intervals, possibly replace filters
3. Engage a specialist company or building services for inspection/maintenance
4. Verify success by follow-up testing

For drinking water from private water supply systems, i.e., from own wells and springs

Contamination due to intervention/repair in the source/spring chamber or well chamber

Contamination after heavy rainfall (ingress of surface water)

Contamination due to construction defects in the source/spring chamber or well chamber (leakage, age-related wear)

1. Thorough visual inspection of the source/spring chamber or well chamber and surroundings
2. Regular inspection of the private water supply, especially after possible weather-related influences (heavy rain, long drought)
3. Carry out the inspections required by the health authority at the specified intervals
4. Engage a specialist company at appropriate intervals for cleaning and disinfection of the source/spring chamber or well chamber
5. Verify success by follow-up testing

For flake ice, crushed ice and ice cubes
Hygiene deficiencies:

in the machine including utensils or

in the connecting hose (inlet water) or

in the distribution network (building installation)

1. Thorough visual inspection of the machines and connecting hoses. This usually also requires disassembling parts of the machines
2. Remove contamination or biofilms
3. Thorough cleaning and disinfection of the machines and components (possibly by a specialist)
4. Thorough cleaning and disinfection of utensils (e.g., scoop)
5. Regularly replace the connecting hose between machine and distribution network
6. Replace contaminated or deteriorated hoses (e.g., brittle, porous) immediately
7. Test the drinking water from the distribution network (before the inlet to the machine)
8. Verify success by follow-up testing

Water dispensers connected to the distribution network (building installation)
Hygiene deficiencies:

in the water dispenser
or
in the connecting hose (inlet water)
or
in the distribution network (building installation)

1. Thorough visual inspection of the water dispenser including connecting hose
2. Remove contamination or biofilms
3. Thorough cleaning and disinfection of the water dispenser (usually by a specialist)
4. Possibly regularly replace the connecting hose between machine and distribution network
5. Replace contaminated or deteriorated hoses (e.g., brittle, porous) immediately
6. Test the drinking water from the distribution network (before the inlet to the dispenser)
7. Verify success by follow-up testing