The periods most at risk

Some periods of the year are more conducive to the development of bacteria than others. Although the risk is present throughout the year, it is vital to test the water of your system during these key periods.

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The seasons and the temperature play a major role in the growth of bacteria and the occurrence of epidemics.

Legionellae can only survive if the temperature of the water is between 25 °C and 45 °C, which constitutes a very serious risk to cold water systems in summer, for example.

Coliform bacteria can contaminate a large number of people via bathing waters which are visited a lot when the weather is warm.

Awareness of the key periods allows you to take action at the right time and prevent the risk before an infection is generated.

prévention du risque légionelle

Periods of absence: a risk to unused installations

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Legionella

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Coliformes

Following a period of absence from a second home, a publicly accessible establishment which is closed during the winter, or even after a time away on holiday, for example, the water which has stagnated in the system during this period can have become contaminated with legionellae, as well as with coliforms in the case of faecal contamination. Stagnant water constitues an ideal breeding ground for bacteria. It promotes the formation of a biofilm, a layer of organic depositions in which bacteria will find the nutrients which are necessary to their growth. Bacteria can therefore multiply until colonies numbering millions of individual bacteria per litre of water are formed. This is why it is essential to check your water after a long period in which the installations are not in use.

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During summer: beware of bathing water, overheating hoses and cooling devices (air conditioning, misting)

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Legionella

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Coliformes

Legionellae

Summer and heat peaks are periods in which most epidemics of bacteriological contamination linked to water are identified. The heat, and particularly temperatures greater than 25°C, promote the steeping of water and the proliferation of legionellae in cold water systems. It can therefore be found at all points of the water system which would be heated over a long period (shower, tap, hosepipe, etc).

Summer is also synonymous with the intensive use of air conditioners or misting apparatuses. If they are badly maintained, these apparatuses can be the source of legionellosis epidemics.

Coliforms

It is during this time too that beaches and bathing waters (communal or private swimming pools) are visited most. Faecal contaminations (intentional or accidental), which are revealed by the presence of coliforms, can therefore infect a very large number of people during this season.

risque de développement des e. Coli après de fortes pluies

Following heavy rain

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Legionella

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Coliformes

Coliforms

During and just after significant precipitation, water flows can transport alluvial deposition loaded with faecal contaminants. These faecal contaminants are thus found very frequently in watercourses, water tables, the sea, bathing waters, private swimming pools, wells, tanks and certain external installations, etc., which presents a considerable health hazard. Moreover, numerous beaches are closed on these occasions to limit the risk of infection during periods of inflow. In case of doubt, it is necessary to test for the presence of coliform bacteria.

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Legionellosis epidemics and the case of contamination of surrounding installations

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Legionella

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Coliformes

Certain infrastructures can generate contaminations of open-air domestic installations. For example, ART (autorefrigerant towers in multiple-dwelling buildings, industrial buildings, factories or medical centres) can be the source of large legionellosis epidemics. In the event of contamination with legionellae, ARTs can spread microdroplets of infected water in a radius of up to tens of kilometres, unleash an epidemic, and contaminate cisterns, outdoor spas, tanks, etc…

For example, in 2018, in Brescia, in Italy, 405 people were hospitalised after contracting legionellosis. The Italian health authorities had checks performed on cooling towers of three companies in the region: nine samples out of ten were found to be contaminated by legionella. This was the case even though there was a prevention policy dedicated to this type of installation.

If you live beside the focal point of an epidemic, testing the water in your external installations (spas, cisterns, tanks used for watering) is a vital preventative measure.

Personnes agées fragiles face au risque legionelle et coliformes

Regularly all year round, above all if people at risk use the system

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Legionella

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Coliformes

Generally, it is recommended that regular maintenance of your system be carried out throughout the year. This maintenance must be suitable for your fixture as well as for the quality of the water. Carrying out monitoring tests regularly, or whenever there is any doubt, is vital in order to ensure that your water system is safe. This is all the more true if there are vulnerable people amongst the users. The elderly, young children, immunocompromised individuals, or people who are convalescing are amongst those deemed to be at risk.

F.A.Q

I have been away for two weeks, do I have to check my water when I get back?

A water system which is not used over a long period presents a serious risk of contamination. Stagnant water, corrosion and scaling create favourable conditions for the proliferation of legionellae bacteria. Upon returning to your home, it is advisable to let the water (hot and cold) flow for several minutes, taking care to protect yourself from splashes, and then test the water, ideally at different outlet points to avoid any risk.

I have a natural swimming pool. What are the risks of contamination?

Any unchlorinated bathing water presents a serious risk of bacteriological contamination, regardless of the system of phyto-purification selected. It is vital to monitor the composition of the water in order to avoid the human or animal faecal contaminations which can occur, as well as any potential contamination with legionellae if the temperature of the water exceeds 25°C, in particular in summer.

Can a chlorinated swimming pool be contaminated?

Even a chlorinated pool can become contaminated if the chlorine concentration is too low. Human or animal faecal contaminations occur very frequently in these installations, whether they are communal or private swimming pools. These can be intentional or accidental, and can come from young children or any other user. The infections can therefore affect all users and can sometimes prove to be very serious for those groups who are the most vulnerable. This is why public swimming pools are subject to daily checks and why it is so vital to check the water of a private swimming pool as often as possible.

Can my cold water be contaminated by legionella?

Yes, in summer, temperatures do often exceed 25°C over a long period. Legionellae develop particularly in water with a temperature between 25°C and 45°C. The frequency of heatwave episodes also increases the risk of contamination of the cold water network. This heat risk is compounded by the risk posed by installations which are little used during the rest of the year, in particular summer kitchens, outbuildings, automatic sprinkler systems or outdoor taps. It is therefore advisable to flush out your system and test it each time it is put back into use.

What should I do in the event of contamination?

This depends on the point of contamination, the pathogenic bacteria responsible, and its level of concentration in the water.
In the event of contamination with legionellae, it is recommended that you contact the manager of the water system in order to have a professional engaged. He/she will carry out a high-temperature heat treatment and/or a chlorine chemical treatment in order to eliminate the bacteria. However, it is very difficult to eradicate legionellae completely. There are frequently recurrences, which make it necessary to regularly monitor your water system once it has been contaminated.
If you suspect you are exhibiting the symptoms of legionellosis (high fever, cough, muscular pain, headaches…), contact your doctor. Depending on the country, legionellosis may be a disease which must be declared by law. For example, in France, it gives rise to a medical and environmental inquiry by the Agence Régionale de Santé (ARS – Regional Health Agency) to identify the source of contamination.

In the event of your running water system being contaminated with coliforms (including E. coli), it is recommended that the water not be used for drinking, cooking or for cleaning teeth. It is advisable to contact the system manager immediately, who will inform you of the protocol to be followed in accordance with the instructions of the responsible health authorities.

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