Legionella: what operators of hot water systems need to know

The changing room at the workshop has six showers. During the three-week summer shutdown, none of them is used. The water sits in the pipes, and in the warm changing room the hot water slowly cools down while the cold water warms up. On the first working day, the early shift takes a shower.

These are exactly the conditions in which Legionella can multiply. The bacteria occur naturally in almost all damp environments. They become a problem when water stands for a long time at a temperature between roughly 25 and 45 °C. People are infected mainly by inhaling fine water droplets — in the shower, for example.

This article explains what food law requires of operators of shower facilities, which temperatures the federal authorities and the industry association recommend, and what a self-monitoring routine looks like that can actually be kept up in day-to-day operations.

Why Legionella is an issue for operators

A Legionella infection can cause a severe form of pneumonia known as Legionnaires’ disease. According to the Bundesamt für Gesundheit (BAG), the risk increases with age; smokers and people with weakened immune systems are particularly susceptible. Anyone who operates showers used by other people therefore bears a responsibility that goes beyond their own household.

Systems with the following are particularly critical:

• hot water cylinders whose temperature has been lowered to save energy,
• pipes supplying showers that are rarely used — guest rooms, changing rooms, emergency showers,
• dead-leg pipe sections left after a refurbishment,
• cold water pipes that run alongside hot water or heating pipes and warm up.

What the law requires

The requirements for shower water are set out in the Verordnung des EDI über Trinkwasser sowie Wasser in öffentlich zugänglichen Bädern und Duschanlagen (TBDV). It applies to shower water in publicly accessible facilities. Under the ordinance, a facility is publicly accessible if it is open to the general public or to an authorised group of people and is not used within a family setting (TBDV Art. 7). The Lebensmittelgesetz cites shower water in hospitals, care homes and hotels as examples. If in doubt as to whether your company’s staff showers fall within this scope, check with the cantonal laboratory.

Three things apply to these facilities:

• A maximum value: shower water may contain no more than 1000 colony-forming units of Legionella per litre (TBDV Annex 5 no. 5).
• Operation in line with good engineering practice: shower facilities must be installed and operated in accordance with recognised engineering practice. The owner has them regularly monitored and maintained by suitably trained persons (TBDV Art. 13).
• Self-monitoring: under the Lebensmittelgesetz, shower water in such facilities is classed as a commodity, and anyone who supplies it is obliged to carry out self-monitoring (Lebensmittelgesetz Art. 5 and 26). This includes verifying the effectiveness of the measures through sampling and analysis and documenting the self-monitoring (LGV Art. 81 and 85).

The law does not lay down a fixed interval for Legionella sampling — such as ‘every year’. Self-monitoring and its verification must be proportionate to the safety risk (LGV Art. 74 and 81). A care home with bedridden residents therefore needs closer monitoring than a workshop with six showers.

Enforcement is the responsibility of the cantons, through the cantonal chemist and the cantonal laboratory (Lebensmittelgesetz Art. 47 to 49). The authority may inspect documents and records (Lebensmittelgesetz Art. 30). Self-monitoring that has not been written down cannot be demonstrated there.

The TBDV does, however, contain one deadline: if the microbiological requirements for water in shower facilities can only be met through structural refurbishment, this must be carried out by 30 April 2027 (TBDV Art. 16 para. 2).

Temperature is decisive

Legionella struggles to multiply in hot and in cold water. The BAG describes the correct water temperature as the best preventive measure. The recommendations of the BAG and the Bundesamt für Lebensmittelsicherheit und Veterinärwesen (BLV) therefore give guide values for operation:

Location	Guide value
Hot water cylinder outlet	60 °C
Pipes kept hot, such as the circulation loop	55 °C
Draw-off point, after running briefly	at least 50 °C
Cold water	no more than 25 °C

The values are taken from Module 11 of the BAG/BLV recommendations ‘Legionellen und Legionellose’. It also recommends recording the temperatures roughly every three months. Lowering the cylinder temperature to cut costs saves energy — but leaves the range the recommendations provide for.

Avoiding stagnant water

The second risk besides temperature is stagnation. The recommendations are specific:

• Showers that have not been used for more than a week are flushed with hot water before they are next used.
• Draw-off points that are normally not used for more than three days belong in a flushing plan and are flushed thoroughly at least twice a week.
• Pipe sections that are no longer needed, known as dead legs, are removed.

For the changing room in the opening example, this means: before the first working day after the holidays, someone runs the hot water at every shower — and writes down when and where.

Self-monitoring in practice

Self-monitoring for shower facilities need not be a hundred-page binder. It consists of just a few building blocks:

1. Hazard analysis: which showers are there, who uses them, which are rarely used, where is the cylinder?
2. Measure temperatures: at the cylinder outlet, in the circulation return and at the most distant shower. Record the result with the date.
3. Keep a flushing plan: for rarely used showers, with a signature or initials.
4. Have samples taken: at intervals appropriate to the risk. The BAG and BLV recommend having samples taken by trained persons and analysed in accredited laboratories.
5. Act on findings: if the value is between 1000 and 10,000 CFU/l, the recommendations speak of moderate contamination: raise temperatures permanently, carry out thermal disinfection with the help of a specialist, and re-test within two months. Above 10,000 CFU/l, refurbishment is required, and the showers are generally taken out of service.

The technical guidelines of the Schweizerischer Verein des Gas- und Wasserfaches (SVGW) — W3/E3 on hygiene and W3/E4 on self-monitoring in drinking water installations — describe these steps in detail. They are available for a fee and are not law; according to the SVGW, they serve the self-monitoring required by law.

Rule of thumb: hot stays hot, cold stays cold, and no water stands still for long. Write down whatever you measure, flush and sample — only with documentation does self-monitoring count as such.

This article is general information and does not constitute legal advice. In individual cases, the regulations and the requirements of the competent authority apply — for shower water, the cantonal laboratory.

How Fristo helps

For recorded drinking water systems and water heaters, Fristo suggests the template ‘Self-monitoring of drinking water system (Legionella)’, with its legal basis and source. A due date is only created once you have confirmed that it applies to your organisation. You file the laboratory report as an inspection record on the work order, and the per-building report shows which checks have been completed and which are overdue.

Sources

• Verordnung des EDI über Trinkwasser sowie Wasser in öffentlich zugänglichen Bädern und Duschanlagen (TBDV), SR 817.022.11, Art. 7, 13, 16 and Annex 5 — Federal Chancellery, Fedlex: fedlex.admin.ch/eli/cc/2017/153/de
• Lebensmittelgesetz (LMG), SR 817.0, Art. 5, 26, 30 and 47 to 49 — Federal Chancellery, Fedlex: fedlex.admin.ch/eli/cc/2017/62/de
• Lebensmittel- und Gebrauchsgegenständeverordnung (LGV), SR 817.02, Art. 74, 81 and 85 — Federal Chancellery, Fedlex: fedlex.admin.ch/eli/cc/2017/63/de
• Legionellosis (Legionnaires’ disease) — Bundesamt für Gesundheit BAG: bag.admin.ch/de/legionellose-legionaerskrankheit
• Shower and bathing water, with the recommendations ‘Legionellen und Legionellose’ — Bundesamt für Lebensmittelsicherheit und Veterinärwesen BLV: blv.admin.ch/de/dusch-und-badewasser
• Legionellen und Legionellose, Module 11 ‘Sanitäre Installationen’ (sanitary installations) — BAG and BLV: blv.admin.ch, PDF
• Legionellen und Legionellose, Module 10 ‘Risikoeinschätzung, Selbstkontrolle, Probenentnahme, Interpretation der Resultate’ (risk assessment, self-monitoring, sampling, interpretation of results) — BAG and BLV: blv.admin.ch, PDF
• Guideline W3/E3 ‘Hygiene in Trinkwasserinstallationen’ — SVGW (industry association): svgw.ch