germs and bacteria

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Updated on: 07.01.2020

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Potentially dangerous pathogens

If you enter the keywords "tap water, boil off, germination" in Google, you will probably get numerous current hits from all over Germany. For although drinking water is one of the most strictly controlled foodstuffs in Germany, one reads relatively often about drinking water contaminated with bacteria and germs, about so-called "official shower bans" for legionella infestation or the urgent request to boil one's tap water.

Germs and bacteria side by side as schematic drawing

Every person consumes several liters of liquid every day with their food or as a drink, a large part of which is drinking water. But even strictly controlled and properly treated tap water still contains millions of germs that can transmit diseases. "Drinking water is not germ-free. Even after proper treatment, it still contains microorganisms," writes the Federal Environment Agency in an article on microbiology. "However, according to the German Drinking Water Ordinance, drinking water may not contain pathogens in concentrations that could endanger human health.
In simple terms, germs or microorganisms are viruses, bacteria and fungi that can have both positive and negative, i.e. pathogenic, effects on people. Up to 200,000 germs can be found in one millilitre of tap water, which can multiply in the water pipes on their way through the public supply network into the building and - favoured by old house pipes and higher temperatures - can lead to a high germ load in the mains. These include, for example, Pseudomonas aeruginosa, Legionella, Enterococci, E. coli and coliform bacteria, which, according to the Drinking Water Ordinance, must not be present in tap water (0 KbE* per 100 ml of water) or only in very small quantities.
As a rule, tap water in Germany is harmless to health. Whether an infection occurs depends on the type of pathogen, the quantity of germs and the health constitution of the individual. Pathogens in drinking water can be dangerous to people in two ways. In most cases, one gets infected by drinking contaminated water, e.g. Pseudomonas aeruginosa, E. coli or coliform bacteria. A special case are legionella, which infect humans by inhaling water vapour contaminated with legionella, for example in the shower.

Faecal germs

E.coli and coliform bacteria, colloquially known as coliform bacteria, are an indication of contamination of drinking water by faeces. The Federal Environment Agency writes that "in recent years a number of "new" pathogens have been added to a large number of known pathogens that can enter the human body with drinking water - such as Salmonella and Shigella - for example Campylobacter, EHEC-Escherichia coli and Noroviruses (...) from human or animal faeces. In risk areas such as the Alps or in low mountain ranges, faecal germs are often still detectable in drinking water supplies even after multi-stage conventional treatment by sewage treatment plants. For example, in 2008 the State Office for Food Safety and Health in Bavaria documented pathogenic faecal germs in almost 10% of all large public water supplies and in about a third of the smaller water supplies. The standard analysis of samples for E. coli and coliform bacteria is usually not sufficient for detection. Such pathogens in drinking water can, for example, trigger infectious diseases with diarrhoea, vomiting and fever, and in some cases even pneumonia.

Those who think they are on the safe side with mineral and table water must be disappointed. The Bavarian State Office for Food Safety and Health has also found many cases of germ contamination in samples of mineral and table water: Up to 13% of the table water bottles and up to 3% of the mineral water bottles examined contained coliform faecal germs.


Enterococci are also an indication of contamination of drinking water by faeces. The introduction of such bacteria into groundwater can be caused by agricultural fertilisers or the faeces of farm animals; precipitation transports them into the groundwater. However, technical faults in the sewage treatment plant or repair work in the public pipeline network can also introduce enterococci into the drinking water.

Enterococci can lead to infections in various parts of the body, especially the urinary tract, but also the abdomen and heart, in people with weakened immune systems. In women, this can lead to inflammation of the fallopian tubes or infection of the bladder. Wound infections and abscesses are also among the possible consequences.

Pseudonomonas aeruginosis

A particularly dangerous bacterium in drinking water is Pseudonomonas aeruginose, which is found almost everywhere and is a natural component in groundwater deposits.
Because it is particularly undemanding and survivable in various environments, Pseudomonas aeruginose is also resistant to most antibiotics or disinfectants. This makes it particularly dangerous for immunocompromised people, for example in hospitals or nursing homes.

In general, Pseudomonas aeruginose is rarely found in drinking water pipes. However, it can get into the cold water pipe system of the house via the house connection pipe and multiply in the biofilm, especially in dead pipes or stagnation of the house installation. Once it has established itself in the pipe system of a house, it can only be removed again with extremely costly measures such as chlorine flushing.

The Drinking Water Ordinance prescribes the strictest limit values for the bacterium of 0 CFU per 100 ml. If Pseudomonas aeruginosa occurs, appropriate measures must be taken immediately, including interrupting the water supply, as the bacterium easily multiplies and, in the worst case, infects the entire pipeline network. Due to climate-induced warming of the groundwater, the distribution of Pseudomonas aeruginosa will increase in the future.

In humans, it can cause various infections or pus formation. Especially for risk groups with weakened immune systems or in case of already existing diseases, an infection with Pseudomonas aeruginosa can cause serious complications such as pneumonia, wound infections and blood poisoning. Although the bacterium is less dangerous for healthy people, infections of the skin, nails, hair roots, the cornea of the eye and inflammation of the auditory canal can be the consequences.

In order to effectively protect its drinking water from Pseudomonas aeruginosa, it is recommended to filter it with an activated carbon block filter as offered by Alb Filter. These are able to filter out the bacteria without themselves becoming infected.


Legionella are rod bacteria and a natural component of the soil and occur in low concentrations in every water supply. From there they are flushed into the buildings where they can multiply strongly with the appropriate nutrient supply and water temperatures of more than 20°C.

Unlike most other pathogens in water, they do not cause infections through their consumption, but when they are inhaled, for example when showering with the water vapour, but also as so-called aerosols - small water droplets - in swimming and steam baths, air conditioning systems, or near cooling towers.

If legionella enters the lungs of an immunocompromised person, it can lead to Pontiac fever as well as to the so-called legionnaires' disease, a severe pneumonia that can be fatal. Especially infants, sick and elderly people belong to the risk groups. According to the Robert Koch Institute (RKI), every year up to 30,000 people in Germany contract this type of legionnaire's disease, and around 1,200 die of it. The number of undetected cases is probably many times higher because legionnaires' disease is often misdiagnosed or not recognized as such. In 2011, the RKI has included Legionella in the group of the 26 most important infectious agents in Germany.

Legionella in cold and warm water systems has therefore been a dominant topic in drinking water hygiene for years. Particularly in old buildings with their often poorly maintained water systems and widely ramified pipe networks, this problem is often encountered. Almost a quarter of all buildings to be tested exceed the limit values of the Drinking Water Ordinance for legionella of 100 CFU per 100 ml of tap water, where CFU stands for "colony-forming unit". The German Drinking Water Ordinance therefore prescribes regular checks of the legionella values, especially for apartment buildings, residential complexes and public buildings. In the worst case, a strong excess can result in an immediate official shower ban. But also sanitary facilities that are used irregularly and in whose pipes water stagnates at possibly increased temperatures, e.g. in holiday flats, hotel rooms, guest bathrooms, sports facilities or mobile homes, are at risk.

Home owners or tenants often have to take action themselves to keep the risk of legionellosis as low as possible. In most cases, attempts are made to limit legionella by flushing the pipe system with high temperatures or chlorine as a countermeasure - but this is insufficient. This is because the temperature of the water in all parts of the pipeline system would have to exceed 60°C over a period of one hour. However, limescale deposits, rust and biofilm in the pipe system form niches and retreat areas and thus prevent effective killing of the Legionella. Because legionella can survive temperatures of 70°C for up to 60 minutes. The conventional method of thermal disinfection to hygienise the pipe system is therefore not reliable.

Learn more about Legionella

Multiresistant germs

Multi-resistant germs are often heard about in hospitals, but such multi-resistant germs have now also been detected in rivers and bathing lakes. Multi-resistant germs are pathogens that have become resistant to drugs such as antibiotics over several generations because they have adapted. This resistance is passed on to the next generation of bacteria and the drug becomes ineffective. Such multiresistant germs arise because antibiotics are used unnecessarily, too often or incorrectly. Multi-resistant germs then enter the environment via the wastewater, survive sewage treatment plants and are discharged into rivers with the treated water. The excessive use of antibiotics in intensive livestock farming also causes multiresistant pathogens to enter fields via the liquid manure of farm animals and from there into water bodies.

How such multiresistant pathogens behave in the environment has not yet been extensively researched, but they certainly pose a risk. While healthy people usually have nothing to fear, seniors, babies and people with weakened immune systems are certainly at risk. However, in order for multi-resistant germs in surface water such as rivers and lakes to reach drinking water, they have to enter the groundwater or bank filtrate. The probability is very low, but this is not excluded.

To effectively filter such multi-resistant pathogens from tap water at home, various technical methods are available, whereby activated carbon block filters such as those of the Alb Filter are particularly suitable.

Parasites in drinking water

According to the WHO definition, parasites in drinking water, especially the parasite species Cryptosporidium parvum and Giardia lamblia, are zoonoses, i.e. diseases and infections that are transmitted naturally by faecal-oral routes between vertebrates and humans. Cryptosporidia and Giardia are also common in Germany. Extensive investigations by the State Health Office of Baden-Württemberg have shown that parasites - albeit in small numbers - can be detected in up to 50 percent of river, lake and karst waters. However, according to the Federal Environment Agency, these "cannot be killed by processes used for drinking water disinfection because they are highly resistant to chlorine".

In rare cases, such parasites can lead to epidemics - for example many years ago in Milwaukee, USA, where cryptosporidia caused severe diarrhoea in more than 400,000 people and even more than 100 people died despite chlorination of drinking water. Particularly in immunocompromised people, such parasite-transmitted diarrhoea can also lead to death.

In Germany, only one case of giardiasis in connection with contaminated drinking water is known to date, although the rules of technology have not been properly observed. However, the Federal Environment Agency cannot completely rule out the possibility of drinking water being contaminated by such parasites. For the treatment of drinking water, it recommends the use of the finest filters for drinking water disinfection in waterworks, but implementation is very hesitant for cost reasons. So if you want to be on the safe side, you should protect yourself with ultrafiltration, for example with Alb Filter with a NANO cartridge.