Legionella: How long to run water?

In principle, legionella are considered harmless. An actual danger for humans only arises when the pathogens are inhaled via the lungs through contaminated water vapor – for example when showering. There, the bacteria can cause, among other things, life-threatening pneumonia – known as Legionnaires’ disease – or Pontiac fever.

But how exactly can the risk of legionella be minimized? Hot water temperature plays an important role in containing the risk of Legionella. In this article you will learn how long you need to run the hot water, what measures protect against water stagnation and where you should pay special attention.

Run hot water for some time

Since Legionella is inevitably present in all natural fresh water, complete elimination of the germs is basically impossible. According to the German Drinking Water Ordinance (TrinkwV) , a quantity of 100 colony-forming units (CFU) per 100 milliliters of water is permissible in groundwater or drinking water. With the help of a special drinking water installation, this legionella value can be regularly checked and maintained.

However, the following conditions can be extremely conducive to the proliferation of legionella, so that they may increase the health risk:

• Cold water temperature above 25 degrees
• Hot water temperature below 50 degrees
• persistent water stagnation

For this reason, a minimum temperature of 55 degrees is required in public buildings as well as in apartment buildings to contain the health risk.

In addition, you can take some measures yourself within the framework of legionella prophylaxis to protect yourself from legionella in the drinking water installation:

The recommended water temperatures in the piping system of at least 50 degrees and a maximum of 25 degrees should not be exceeded or fallen below.

The taps, such as faucets, should be used regularly to prevent the water from cooling down or heating up.

Accordingly, running the water is a good way to stop the proliferation of legionella in drinking water.

However, since high water temperatures of over 60 degrees can be very expensive in the long run, you can alternatively install a so-called legionella circuit . This heats the hot water in the water tank once a week to over 60 degrees – preferably 70 degrees – so that any legionella present is killed.

These measures protect against water stagnation

Just like water temperature, water stagnation can also promote the development and multiplication of health-threatening bacteria.

To prevent the water in the water pipes from standing still for too long, experts advise ensuring that the water is completely replaced once every 72 hours at least. In a one- or two-family house, showering or simple flushing should be sufficient for water replacement.

Thus, about 80 to 100 liters of water are consumed per eight-minute shower . With a storage capacity of about 200 to 300 liters of water, short showers are therefore an ideal measure to prevent water stagnation. In order to flush the piping section of the faucets, one should let the water run for about 10 to 20 seconds.

Contrary to popular belief, however, Legionella can also multiply in cold water above 20 degrees. For this reason, any cold water pipes should be insulated so that the drinking water cannot be heated up so quickly by external influences.

According to experts, completely unused taps should be disconnected at the outlet of the main pipe . This is the only way to prevent water from standing in the pipes and the pathogens from settling and multiplying there.

The Legionella comfort zone

Although Legionella live in all freshwaters, they have preferred breeding sites. Especially unused showers and faucets provide the optimal conditions for bacterial growth due to the stagnant water. This is always the case when buildings are being renovated, for example, or are simply not being used due to vacations or other seasonal circumstances.

In addition, excessively large water pipes can also provide an optimal comfort zone for Legionella. With large pipes and reduced water usage, not all parts of the pipes may be used, which can also cause the water to stagnate. A long period of time between the construction of the pipes and the actual activation of the pipe network can also promote legionella growth.

Thus, water stagnation in the pipes and conduits basically always represents an increased risk to health, as microbial growth as well as the formation of a so-called biofilm is optimally promoted. The ideal temperatures can further accelerate the growth of such health-threatening bacteria.

Watch out for vacation homes

Vacation houses and apartments are usually used only seasonally. Outside the vacation or vacation season, the cottage remains unused – as well as the water pipes. Few landlords know about legionella formation due to water stagnation, so extra caution is needed when on vacation.

To minimize the risk of serious illness, run the water before using the faucets. The best way to do this is to turn the taps on completely for a few minutes with hot water. In this way, the pipes to the wash basin and sink, as well as to the shower, are flushed hot through once.

For longer trips, you should ask the housekeeper to run the water every three days. This way, the water in the pipes is also replaced regularly during the vacation, so that possible infections are less likely to occur upon return. Should the trip last more than four weeks, it is advisable to follow the recommendations of TÜV Nord : In this case, the main tap should be turned off completely and the pipes flushed with hot water for a few minutes after returning home.

FAQ

How long is the water allowed to stand in the pipe?

To prevent legionella, the water in the pipes should be completely replaced after 72 hours at the latest.

How long to run water after vacancy?

After a long idle period, the water should be left running for at least a few minutes until the water reaches a constant temperature.

How long does it take for legionella to die?

At a temperature of 50 degrees, about 90 percent of the bacteria die within one and a half to two hours, depending on the genus. At 60 degrees, the pathogens are even killed within half an hour. To kill the germs within a very short time (about two minutes), a water temperature of over 65 degrees is required.

How do I get legionella out of the water pipe?

Basically, heating the entire water-carrying systems to at least 70 degrees is a safe way to kill Legionella in drinking water. Due to a special legionella circuit, this happens quite automatically once a week.

Conclusion

Legionella are found in all fresh water – so also in the water pipes of buildings and eventually in our drinking water. A particularly high health risk is usually posed by the inhalation of contaminated water droplets during the generation of water vapor.

To prevent legionella in drinking water, the water should be heated to over 60 degrees at least once a week. In addition, water stagnation should be prevented at all costs, so regular flushing of all pipes is an important part of legionella prophylaxis. This is the only way to protect health in the long term. Anyone who is unsure should install a legionella filter.