Legionella Water Temperature: When does legionella grow and how do you measure it?
- , by Luc Krijnen
- 4 min reading time
Legionella is a bacterium that can cause serious health problems, such as Legionnaires' disease. Therefore, strict rules apply in the Netherlands for legionella prevention and the temperature of drinking water installations.
The correct water temperature plays a crucial role in legionella prevention and control. When water is too warm or stands still for too long, the bacteria can multiply rapidly.
In this comprehensive guide, we explain:
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at what temperature legionella grows
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how to measure legionella temperature
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which water temperatures are safe
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what the legionella regulations in the Netherlands prescribe
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how to conduct a legionella risk analysis and management plan
Special measuring instruments are often used for checking water installations. For example, check out the range of legionella thermometers and measuring equipment for professional legionella monitoring.
What is legionella?
Legionella is a bacterium that occurs naturally in water and soil. In small quantities, this usually poses no problem, but under certain conditions, the bacteria can multiply rapidly.
Legionella mainly grows in drinking water installations, such as:
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hot water pipes
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showers
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boilers
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hot water tanks
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cooling towers
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jacuzzis
Infection occurs when people inhale water droplets (aerosols) containing legionella. Therefore, it is important to carry out legionella inspections and legionella controls in water installations.
At what temperature does legionella grow?
The temperature of water is the most important factor for legionella growth.
| Water Temperature | Effect |
|---|---|
| < 20°C | Legionella hardly grows |
| 20 – 25°C | limited growth |
| 25 – 45°C | ideal growth temperature |
| 50°C | growth stops |
| 55°C | bacteria slowly die off |
| 60°C+ | legionella is killed |
This means that lukewarm water between 25°C and 45°C poses a significant risk for legionella growth.
Therefore, it is important to regularly measure the legionella water temperature.
For an accurate measurement, installers often use a professional legionella thermometer.
Dutch legionella regulations
In the Netherlands, rules for legionella prevention are laid down in various laws and standards:
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Drinking Water Act
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Drinking Water Decree
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Legionella Prevention Regulation
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NEN 1006
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ISSO 55 guidelines
These rules oblige owners and managers of buildings to carry out legionella risk analyses and legionella management plans.
They must also regularly:
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carry out legionella inspections
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measure legionella temperature
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perform legionella monitoring
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have legionella water tests performed
Priority institutions
Some buildings have an increased legionella risk. Therefore, stricter rules apply here.
Examples of priority institutions:
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hospitals
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healthcare institutions
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hotels
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campsites
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saunas
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swimming pools
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marinas
These organizations are obliged to have a legionella risk analysis and legionella management plan.
Legionella temperature hot water
Strict temperature rules apply to hot water.
According to Dutch guidelines:
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minimum 60°C in boilers
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minimum 55°C at tap points
These temperatures ensure that legionella cannot grow.
Therefore, it is important to regularly measure the legionella temperature of hot water with a reliable legionella thermometer.
Legionella temperature cold water
Cold water also plays an important role in legionella prevention.
The guidelines advise:
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ideally below 20°C
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maximum 25°C
When cold water becomes warmer than 25°C, legionella can develop.
Therefore, installers regularly perform legionella temperature measurements in cold water installations.
Thermal disinfection against legionella
A commonly used method to combat legionella is thermal disinfection.
In this method, the water is temporarily strongly heated and flushed through the pipe system.
| Temperature | Minimum flushing time |
|---|---|
| 60°C | 20 minutes |
| 65°C | 10 minutes |
| 70°C | 5 minutes |
This method is often used after a legionella water test where contamination has been detected.
Important legionella prevention measures
Good legionella management consists of several steps.
Regular flushing
Pipes that are used infrequently must be flushed regularly to prevent stagnant water.
Avoid stagnant water
Legionella grows faster in stagnant water. Therefore, installations must be designed with:
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good flow
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minimal dead legs
Measuring legionella temperature
Regular temperature measurements are essential for legionella prevention.
With a professional legionella thermometer, it can be quickly checked whether an installation complies with legal requirements.
Legionella and heat pumps
Heat pumps are increasingly used for hot water.
The problem is that many heat pumps produce water around 40°C, which is precisely in the growth range of legionella.
Therefore, many systems have an automatic legionella cycle where the water is periodically heated to 60°C or higher.
Conclusion
Legionella poses a serious health risk if water installations are not properly managed.
Important measures are:
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keep cold water below 25°C
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hot water above 55°C at tap points
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boilers at least 60°C
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avoid stagnant water
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regular legionella inspection and control
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regular legionella temperature measurement
By combining these measures with reliable temperature measurements and legionella monitoring, the risk of legionella can be significantly reduced.
For professional temperature measurements, you can use legionella thermometers and measuring instruments specifically designed for legionella control.
