Which germs can be in our drinking water?

Our drinking water is not germ-free despite strict controls. In small amounts, most germs are harmless. What dangerous pathogens can still occur in our drinking water, what damage they can cause under what circumstances, and where there is an increased risk, is explained here.


In strictly controlled German drinking water germs are found only in very small quantities. It can be assumed that only at a hundredfold exceeding of the applicable limit values ​​there is an infection risk at all. In addition, out of many germs only a few strains are dangerous to human health at all.

Bacteria always live in and on us, the normal bacterial load of an adult man makes a total weight of several kilograms. We need a variety of these microorganisms to be able to live at all.

There is a risk of disease whenever bacteria multiply excessively in favorable conditions. Which strains can be dangerous to health is also shown in the following list.

The most dangerous bacterial strains

Here is an overview of potentially dangerous pathogens that can (and usually are) also present in drinking water.

Coliform germs

They have their name because of their similarity with Escherichia coli, a gut germ, which also occurs naturally in humans. However, individual strains can cause bacterial dysentery and severe diarrhea. As one of the few types of germs coliform germs in drinking water should not occur at all.


These are also intestinal germs, which mainly point to contamination with fecal matter which occurred some time ago. Among other things, they can cause wound infections and urinary tract infections.


They occur not only in spoiled food, but often in nature. They can also be present in groundwater and drinking water. However, this represents a very high risk. Salmonella cause severe stomach and intestinal diseases.


Clostridia are also intestinal germs. A single strain, Clostridium perfringens, can cause the so-called gas gangrene, an extremely dangerous infection of soft tissue. For C. perfringens, the Drinking Water Ordinance therefore has its own, precisely regulated detection method.


Legionella are very dangerous pathogens, which can cause both gastrointestinal diseases and often fatal pneumonia. But they have to get into the lungs by atomizing the water.


Pseudomonas aeruginosa is a germ often found in standing sewage. He can sometimes cause severe infections. This affects almost exclusively people with a limited immune system.

Special risks

Stagnant water, high concentrations of bacteria such as in water filters and deposits in pipes pose particular risks for microbial contamination and subsequent infection. Infants, children and the elderly or ill usually suffer from a weakened immune system and are therefore particularly susceptible to infections.

Tips & Tricks

A sterilization of drinking water is only necessary where a high occurrence of individual bacterial species is detected. Within the valid limits, tap water is safe.

Video Board: How Germs Spread | Explaining the Science for Kids