Fact sheet on Escherichia coli (E. coli) in drinking water

General information
Escherichia coli (E. coli) belongs to the family Enterobacteriaceae and is a natural inhabitant of the intestines of humans and animals. Due to the long survival capability in the environment and in biofilms, the mere occurrence of E. coli does not necessarily indicate a fecal contamination. However, fecal contamination must be considered.
The Drinking Water Ordinance requires the absence of E. coli (0 CFU/100 ml). If E. coli is detected, appropriate countermeasures must be implemented immediately. A positive finding of E. coli in a drinking water sample under the Drinking Water Ordinance must be reported to the competent authority.

Characteristics

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

Origin / Occurrence

• Natural inhabitant of the intestinal tract of humans and animals
• Due to the long survival capability of some strains, E. coli bacteria can also be found in soil and in surface waters

Significance

• Hygiene indicator for serious hygiene deficiencies, possibly also fecal contamination
• Indicator for potential health hazards from certain E. coli strains (e.g. STEC/EHEC) which can cause severe and sometimes fatal illnesses

Growth conditions

• Temperature:
  • Optimum: +30 °C to +37 °C
  • Minimum: +7 °C
  • Generally no growth above +50 °C
• pH value: growth at 4.4 to 9.0
• Water activity (a_w): growth at high water activity of at least 0.95
• Oxygen requirement: growth with and without oxygen (facultative anaerobe)

Inactivation by heating

• At +72 °C for at least 2 minutes exposure time (Attention: monitor core 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 final section of the water outlet after cleaning
4. Verify effectiveness by follow-up testing

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

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

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

Contamination due to intervention/repair in the spring head/well chamber

Contamination after heavy rain (contamination by surface water)

Contamination due to structural defects in the spring head/well chamber (leakage, age-related deterioration)

1. Thorough visual inspection of the spring head/well chamber and surroundings
2. Regular inspection of the private water supply system, especially after possible weather-related influences (heavy rain, prolonged drought)
3. Perform periodic checks required by the health authority
4. Engage a specialist company at appropriate intervals for cleaning and disinfection of the spring head/well chamber
5. Verify effectiveness by follow-up testing

For flake ice, crushed ice and ice cubes
Hygienic 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 machines and connecting hoses. This usually requires disassembling parts of the machines
2. Remove contamination or biofilms
3. Thorough cleaning and disinfection of machines and components (possibly by a specialist company)
4. Thorough cleaning and disinfection of utensils (e.g., scoop)
5. Regularly replace the connecting hose between the machine and the distribution network
6. Replace contaminated connecting hoses or hoses in poor condition (e.g., brittle, porous) immediately
7. Test the drinking water from the distribution network (before the inlet to the machine)
8. Verify effectiveness by follow-up testing

Water dispensers connected to the distribution network (building installation)
Hygienic 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 the connecting hose
2. Remove contamination or biofilms
3. Thorough cleaning and disinfection of the water dispenser (usually by a specialist company)
4. If necessary, regularly replace the connecting hose between the machine and the distribution network
5. Replace contaminated connecting hoses or hoses in poor condition (e.g., brittle, porous) immediately
6. Test the drinking water from the distribution network (before the inlet to the water dispenser)
7. Verify effectiveness by follow-up testing