What does the regulation say?

What is legionellosis? How can the spread of the bacteria be prevented? What are the regulations? Who is affected? Find the answers to these questions in this article.

What is legionellosis?

Legionellosis is a respiratory infection caused by a bacterium of the legionella family.

The infection is caused by inhalation of contaminated water in the form of aerosols or droplets.

This bacterium develops in fresh and stagnant water with a temperature between 25 and 45°C.

Santé publique France, indicates that over the last 5 years:

11 à 13%

cases of legionellosis have been linked to visits to hotels and tourist residences and campsites.

6 à 8%

are related to the use of health facilities.

4 à 5%

are linked to the use of social and medico-social institutions for the elderly (EHPAD).

How can the spread of this bacterium be prevented?

In order to limit the risks, it is therefore necessary to maintain the temperature of the water at at least 55°C, between the point of distribution and the point of use. This is the threshold below which legionella proliferates in the event of contamination.

What factors favour the proliferation of legionella?

The development of this bacterium in Domestic Hot Water (DHW) systems can be the result of several factors:

  • complex and time-consuming DHW installations that encourage water stagnation in the pipes,
  • DHW systems that are used periodically or remain unused for long periods of time.

What is required by law to combat the spread of the bacteria?

In order to fight against the proliferation of the deadly legionella bacteria, the french law imposes since 2010 (decree of February 1st, 2010) a strict control of the temperature in domestic hot water networks (DHW), in all the Health Establishments (Hospitals, EHPAD) and Establishments Receiving Public (ERP).

All these establishments are therefore legally obliged to take measures to monitor and control the DHW networks in order to act as quickly as possible in the event of detection of non-compliance with the temperature thresholds to be checked.

Who is concerned by the monitoring of their domestic hot water system?


Health establishment


EHPAD, Retirement homes


Hotels / Leisure




Other ERP

The establishments concerned are those with a collective distribution of DHW and those that expose the public to water use points that emit aerosols that can disperse legionella:

  • all health care institutions,
  • residential facilities for the elderly (EHPAD, retirement homes),
  • other social and medico-social establishments,
  • remand centers, prisons, detention centers or semi-liberty centers,
  • hotels, tourist residences, campsites,
  • thermal establishments,
  • aquatic complexes,
  • university halls of residence, colleges and high schools with sanitary blocks with showers for public use (pupils), youth centers with sanitary blocks, with showers for public use (children),
  • open-air establishments.

Find the complete list in the circular Circulaire DGS/EA4 no 2010-448 of 21 December 2010 (pages 5-6).

The most risky installations are showers in hotels, tourist residences and campsites, spas, thermal baths, cooling towers used for air conditioning and collective misting systems (outdoor showers, fountains, etc.).

How often should the domestic hot water (DHW) system be checked?

The control is carried out on a regular basis according to the following rhythm (source: Guide technique de l’ARS):

Monitoring points

Mandatory measures

Monitoring points

Outlet for domestic hot water production(s) (distribution)

Mandatory measures

Water temperature: once a month

Monitoring points

Bottom of hot water production and storage tank(s)

Mandatory measures

Legionella analysis: once a year
– in the last tank if the tanks are installed in series
– in one of them if the tanks are installed in parallel

Monitoring points

Most representative point(s) of use in the network or, failing that, the point(s) of use furthest from the domestic water production

Mandatory measures

Legionella analysis: once a year
Water temperature: once a month

Monitoring points

Loop return (general return) if applicable

Mandatory measures

Legionella analysis: once a year
Water temperature: once a month for each loop


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