Drinking water hygiene is important. If water quality is not right, this has a direct impact on our well-being and the health of each individual. Particularly sick people and persons suffering from an immune deficiency are endangered by contaminated drinking water and domestic water. In sensitive and large objects, such as schools, sports facilities, hotels and homes for the elderly, the probability of users becoming infected with contaminated drinking water is relatively high.

Why is drinking water hygiene important?

Water is the elixir of life - and of particular importance to us: the human body consists of about 70 percent water. It supports vital functions of our organism such as metabolism, digestion, cardiovascular and warmth. Regular drinking is therefore essential for health, well-being and performance. The high quality of drinking water is correspondingly important. It must be drinkable and usable at all times without hesitation.

In the worst case, these bacteria lead to acute health hazards, which can lead to further consequences for operators of large properties:

  • Negative reporting
  • Loss of earnings
  • Closure of buildings
  • Cost-intensive refurbishment
  • Criminal penalties

A dramatic historical example is the cholera epidemic in Hamburg in 1892, this clearly shows how important clean drinking water is to the health of the population. At that time the drinking water for the Hanseatic city was removed from the Elbe without filtering. The low water level of the river caused contamination of the central water supply with faeces and cholera vibrios. The subsequent epidemic resulted in 8,605 death victims, nearly 17,000 people fell ill.

What causes drinking water contamination?

The most frequent causes are stagnant water in pipelines and bacteria growth-promoting temperatures. Unused pipes must therefore be dismantled, and the temperatures in the water distribution should be constantly monitored. For example, the temperature in the hot water installation should not drop below 50 °C and cold water should not be allowed to heat above 25 °C. An overview of all preventive measures can be found under the menu point Prevention.

How can the drinking water quality be assessed?
Assessment of drinking water quality

The drinking water quality can be assessed with the material parameters, and by determination of the microbiological quality.

The material parameters include the chemical composition and organoleptic parameters - sensual perceptible properties - such as smell, taste, colour and opacity.

The assessment of the microbiological quality of drinking water serves the detection of germs and pathogenic bacteria. In addition, there are specifications for physico-chemical parameters such as conductivity, pH and oxidisability.

To assess the drinking water quality, the colony number is today being increasingly determined. This means that all bacteria are detected in the drinking water and provide proof of the quality of drinking water, especially since more than 90% of the bacteria are in the biofilm on the installation surface.

Increased colony numbers point to increased biofilm growth. The limit values at the dispensing point of the user are 100 colony forming units / ml.

  • Colony number at 22°C = 100 / 1 ml
  • Colony number at 36°C = 100 / 1 ml

For increased colony number values the causes have to be determined and corresponding hygienic measures have to be taken. There is no direct relationship between the colony number values and the detection of disease-inducing bacteria.

An extract of the most important chemical and chemical-physical parameters is given here, with the limit values based on the German Drinking Water Ordinance (TrinkwV 2001 + Amendment Nov. 2011): 

Chemical-physical parameters

Limit value


No max. defined


max. 2,500 μS/cm at 20 °C


6.5 to 9.5


5 mg O2 / l

Chemical parameters

Limit value mg / l























Chemical parameters

Limit value mg / l























Which pathogenic bacteria are spread in drinking water?

An increased number of bacteria in the drinking water can pose a great danger to health. Where clean drinking water flows from the taps, bacteria can still enter the drinking water installation unnoticed.

If the bacteria fine safe havens (unused pipelines or defective seals), they can multiply and contaminate the drinking water. It can be particularly critical if the bacteria are disease-causing bacteria and temperatures of 25 ° to 45 °C are set during building operation or long periods of stagnation occur. Regular sampling can provide clarity.

Reported legionellae infections due to travelSource: European Legionnaires’ Disease Surveillance Network (ELDSNet)

The most common pathogens that occur in drinking water installations and can multiply there are the following three:

Legionellae can enter the lungs via the water vapor and cause a life-threatening infection there. They weaken the immune system and lead to death in the worst case if untreated.

Pseudomonas aeruginosa occurs in waste water and finds its way into drinking water due to insufficient hygienic measures. Because of its multiple resistance to antibiotics, diseases that are triggered the germ are difficult to treat. In Germany it is one of the most frequent hospital germs.

Escherichia coli often leads to nausea, vomiting, fever and diarrhoea in infants, pregnant women and the elderly. The germ can get into drinking water due to storms, agricultural wastewater or industrial wastewater.

Where is Legionellae found?

Legionellae can be found in all waters around the world. In the natural environment, however, they exist only in a small number. They feel particularly well in the environment with other bacteria and multiply particularly well at temperatures between 25 ° and 45 °C and are therefore very frequently in the hot water distribution of the drinking water installation. The contents of the water heater or storage tank should therefore be replaced once a day. In addition, the temperature in the hot water distribution should not drop below 50 °C. Also, unused pipe lines, in which the water stagnates and can heat to over 25 °C, are breeding grounds for legionellae. The pathogen can contaminate the remaining drinking water installation from there.


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