Legionella in Water – Risks, Symptoms and Protection for Your Home
- What is Legionella?
- Occurrence and growth of Legionella
- Transmission of Legionella
- Clinical picture & Legionella symptoms
- Prevention & measures against Legionella
- Legal aspects: obligations of landlords
- How can I test my water for Legionella?
- FAQ – Frequently asked questions
1. What is Legionella?
Legionella (Legionella pneumophila) are rod-shaped bacteria that occur naturally in freshwater, lakes and rivers. They were named after an outbreak at an American Legion convention in Philadelphia in 1976.
In low concentrations, they are usually unproblematic. It becomes critical when they multiply significantly in technical water systems such as hot water systems, air conditioning systems or whirlpools.
Are Legionella visible in water?
No. Legionella cannot be seen with the naked eye. Neither the colour, smell nor taste of the water changes. Only a laboratory analysis provides clarity.
Good to know
There are more than 60 known Legionella species and more than 70 serogroups. Legionella pneumophila serogroup 1 is particularly relevant.
Classification
- Genus: Legionella
- Most important species: Legionella pneumophila
- Cell shape: Rod-shaped
- Gram stain: Gram-negative
- Mode of life: Intracellular
- Natural habitat: Freshwater and moist soils
2. Occurrence and growth of Legionella
In nature, Legionella occur in low concentrations. They become dangerous mainly in artificial water systems when several conditions come together:
How quickly do Legionella develop?
At optimal temperatures of 35–37 °C, Legionella can double every 2–6 hours under ideal conditions. Within a few days, this can lead to very high bacterial counts.
Temperature & growth
Risk-prone locations
- Hot water storage tanks: high risk due to stagnant water and critical temperatures
- Shower heads and fittings: high risk due to biofilm and aerosol formation
- Rarely used pipes: high risk due to stagnant water
- Cooling towers: high risk due to large aerosol release
- Whirlpools and spas: medium to high risk due to warm temperatures and aerosols
- Cold water pipes below 20 °C: lower risk, provided the temperature remains consistently low
Do you know whether your hot water system is safe?
With a professional Legionella test, you gain clarity about the contamination of your water.
3. Transmission of Legionella
Legionella are not transmitted from person to person. Infection occurs by inhaling aerosol containing Legionella, meaning the finest water droplets in the air. Drinking contaminated water usually does not lead to illness.
- Contaminated hot water
- Aerosol formation, for example when showering
- Inhalation of the finest water droplets
- Possible infection of the lungs
Particularly at risk
Older people, smokers, people with weakened immune systems as well as people with chronic lung diseases or diabetes have an increased risk.
4. Clinical picture & Legionella symptoms
An infection with Legionella can cause two different clinical pictures: Pontiac fever, which is usually mild, and the significantly more severe Legionnaires’ disease.
Pontiac fever
- Fever
- Headache and aching limbs
- Fatigue and malaise
- Usually self-limiting
- No pneumonia
Legionnaires’ disease
- High fever
- Cough
- Shortness of breath or chest pain
- Nausea or diarrhoea
- Confusion or drowsiness
The incubation period ranges from a few hours to several days, depending on the clinical picture. Legionnaires’ disease is a form of pneumonia and must be treated by a doctor.
Important
In case of high fever, cough or shortness of breath after possible contact with contaminated water, medical advice should be sought promptly.
5. Prevention & measures against Legionella
Legionella can be well controlled through technical and operational measures. The decisive factors are mainly the correct temperature, regular use of pipes and proper maintenance.
Prevention measures step by step
- Set hot water temperature correctly
Set the boiler to at least 60 °C and check regularly. - Avoid stagnation
Regularly flush rarely used outlets and avoid pipes that are no longer needed. - Clean shower heads and fittings
Regularly descale and clean shower heads, as biofilm can form there. - Take water samples
A laboratory analysis is especially recommended in apartment buildings, hotels, care homes or businesses. - Ensure professional planning
Short pipe routes, good insulation and no dead legs significantly reduce the risk.
6. Legal aspects: What are landlords obliged to do regarding Legionella?
In Switzerland, landlords and property owners have a duty of care for drinking water quality. The water installation must be operated and maintained in such a way that no health hazard arises.
Obligations of the landlord
If Legionella levels are elevated, suitable measures must be taken. Depending on the situation, these include thermal disinfection, informing the affected persons, investigating the cause and, if necessary, follow-up testing.
- Food Act: Drinking water must be suitable for consumption.
- Foodstuffs and Utility Articles Ordinance: regulates requirements for drinking water.
- SVGW W3: technical requirements for drinking water installations.
- SIA 385/1: specifications for the planning and operation of hot water systems.
- Cantonal requirements: may contain additional requirements.
If a landlord fails to meet this obligation and health damage occurs as a result, liability issues may arise. Regular Legionella tests help to document the duty of care in a traceable manner.
7. How can I test my water for Legionella?
Legionella are neither visible nor detectable by smell. A professional laboratory test is therefore the most reliable method for detecting contamination.
How a professional Legionella test works
- Plan sampling
For reliable results, suitable sampling points should be defined. - Choose the correct sampling points
Typical points are the boiler, shower, hot water pipe and rarely used outlets. - Analysis in the laboratory
The sample is examined microbiologically and reported as CFU per 100 ml. - Derive measures
If values are abnormal, the cause, temperature management and installation should be checked.
Have your water tested for Legionella
With a professional Legionella test, you gain clarity about the contamination of your water.
8. FAQ – Frequently asked questions about Legionella in water
Are Legionella in water dangerous?
Yes. Legionella can cause severe pneumonia. Older people, smokers and people with weakened immune systems are particularly at risk.
How quickly do Legionella develop in water?
Under favourable conditions such as warm, stagnant water and biofilm, Legionella can multiply significantly within a few days.
Are Legionella visible in water?
No. Legionella change neither the colour, smell nor taste of the water. Only a laboratory test provides clarity.
What symptoms can occur?
Possible symptoms include fever, cough, shortness of breath, headache and aching limbs as well as a general feeling of illness. In case of severe symptoms, medical advice should be sought.
What should be done if a Legionella test is positive?
Affected outlets should not be used as a precaution. Afterwards, specialists should inspect the system, initiate suitable measures and carry out follow-up testing.
What temperature kills Legionella?
High temperatures significantly reduce Legionella. Sufficient hot water temperature is therefore a central part of prevention.
Does the landlord have to pay for the Legionella test?
In rental properties, the owner or landlord is generally responsible for the safe operation of the water installation.
Protect your water quality – request a Legionella test now
Professional analysis, clear results and support in case of abnormal findings.
✔ Legionella, heavy metals and pollutants
✔ For general drinking water and softeners
✔ Risk of transmission during showering
✔ Causes Legionnaires' disease