The colony count is an indicator of the general microbiological load of the water without any further indication of the presence of pathogens.
In each case, 1 ml of water sample is placed on a culture medium and incubated at 22 °C and 36 °C for 48 hours. The colonies that have developed are counted at 6-8x magnification. The incubation temperature gives an indication of the origin of the bacteria. At 22 °C, the majority of germs grow, which are found everywhere in the environment, originate from the soil and can form post-germination or slimy coatings in pipes. At 36 °C, heat-loving bacterial species develop, indicating putrefactive processes in the soil and possibly fecal matter.
For both colony counts, the TrwVO has a limit of 100, i.e. completely germ-free water is not necessary from a health point of view.
Common causes of elevated colony counts are calcified/contaminated aerators/strainers in the faucet, infrequently used faucets, broken pipe sections, poorly maintained water filters, or recent installation work on the household plumbing system. Preventive, regular cleaning of the aerator is highly recommended.
The Drinking Water Ordinance requires that drinking water be free of pathogens. This requirement is considered to be met if neither E. coli nor coliforms are detected in 100 ml of drinking water. Both parameters are indicators of whether the water is contaminated with germs from human or animal feces or other origins.
Coliform germs multiply rapidly.
Many species of coliform germs are part of the intestinal flora and important for digestion. However, there are also species (e.g. Ehec) that release toxins and can thus weaken or damage the body. For example, the function of the intestinal mucosa can be disturbed and diarrhea can be caused. If such germs get into the bloodstream or lungs, bacterial infections can occur. Regular monitoring of well water is recommended, especially in rural areas with intensive livestock farming.
Enterococci are spherical bacteria found in the large intestine flora of humans, mammals and birds. Because enterococci cannot multiply in water, but only in the body, they are a definitive indicator of fecal contamination of water. Therefore, a positive result raises the suspicion that other pathogenic contaminants are present. Unlike coliform bacteria, enterocci are much more resistant to environmental influences or disinfectants such as chlorine. Their occurrence therefore indicates hygienic problems that have been present for some time.
According to the TrwVO, no enterococci may be detectable in 100 ml of sample.
Enterococci can cause wound and urinary tract infections in persons with weakened immune systems. It is also problematic that various strains of enterococci develop resistance to antibiotics.
In case of a positive finding, only boiled water should be drunk.
The cause of the occurrence of enterococci is often long stagnation times of water in the piping system, which leads to the formation of biofilms.