The installations to be tested
All drinking water is exposed to a risk of bacteriological contamination. Monitoring certain specific points in the water system, or certain installations which are more sensitive, is essential to ensure the safety of users.
Artificial water systems are particularly conducive to the proliferation of legionellae. Oxygen, limescale (rich in calcium), corrosion (rich in metallic ions), the presence of a biofilm (a layer of organic depositions on the walls of the system which is rich in nutrients), and the temperature are all factors which are conducive to their growth and their development. All water points in the home are affected by this risk. They require extreme vigilance and regular maintenance suitable for the quality of its water.
Coliforms (including E. coli) are the sign of an animal or human faecal contamination. They are found to be present above all in bathing water, water tanks or wells.
Legionellae develop particularly in water with a temperature between 25°C and 45°C. Hot water tanks, showers, taps and hot tubs (or balneo baths), are therefore installations at highest risk.
In the hottest countries, the summer temperatures are very often greater than 25 °C. They make the cold water system just as exposed to the risk as the hot water system.
Fostered by these good conditions, legionellae can multiply until colonies numbering millions of individual bacteria per litre of water are formed. Once legionellae are inhaled via splashes or water vapour, legionellae come to be lodged in the lungs until an infection is generated.
A coliform contamination in these installations indicates a fault in the system for purifying and treating the water system. In case of ingestion, gastrointestinal infections of greater or lesser severity can arise. According to the WHO, the threshold for potable water which cannot be exceeded is 0 in 100 mL.
Spas, hot tubs, and other jacuzzis combine all the conditions which are favourable to the growth and development of these bacteria. Hot tubs and the water vapour which they diffuse are particularly conducive to the inhalation of contaminated microdroplets.
All bathing installations (fresh water or sea water) are at risk. Cases of faecal contamination occur frequently. Whether they are those of human origin, notably during bathing by young children, or of animal origin (for open outdoor installations), these contaminations can be revealed by the presence of coliforms in your water. The infection can occur following ingestion or contact of the water with the mucous membranes during bathing.
If badly maintained, air-conditioning and misting systems may become devices which are particularly conducive to the development of legionellae. They are therefore all the more dangerous because the risk of contamination can affect a large number of people at the same time via the propagation of microdroplets of contaminated water which are then inhaled.
In the case of air conditioners, the water which circulates inside to cool the air forms an ideal home for legionellae colonies. For misters which are not connected to running water, the stored water is often not replaced enough. Since it is subject to temperature variations from the exterior, it becomes very conducive to the growth of legionellae which are then diffused directly onto the users.
Any stagnant water source represents a serious risk of bacteriological contamination which needs to be monitored regularly. Since it is subject to temperature variations from the exterior, the stagnant water from a well or a tank will heat up and then cool down again, and then heat up again… These variations promote the formation of a biofilm and the growth of legionellae. They can therefore grow to several millions of individuals per litre of water once the right conditions come together. The contaminated water therefore becomes harmful to health if it is vaporised or projected (example: sprinkler water).
Likewise, the water from these installations is exposed to a real risk of contamination with human or animal feces and therefore to the development of coliform bacteria (including E. coli).
Legionellae present no, or very little, risk in these environments.
Bathing waters such as at beaches, rivers and lakes can be infected by faecal bacteria. Whether this is caused by a fault in the purification system for wastewater which is dumped into these water courses or into the sea, or is down to poor hygiene of an excessively large number of users, beaches are closed to bathers each year due to this type of pollution. Coliform contamination occurs by ingestion or by contact with the mucous membranes while bathing.
How can the water in my system be contaminated?
The bacteria are naturally present in the environment. However, a greater concentration than normal can occur if certain favourable conditions come together.
In the case of legionellae, the corrosion and limescaling of the system promotes the creation of a biofilm on the walls of pipes. This is a layer of organic deposition containing nutrients which are necessary for their development. This biofilm is a good breeding ground for the proliferation of legionellae if the temperature of the water is between 25°C and 45°C.
Stagnant water therefore constitutes extremely favourable ground for the formation of legionellae colonies.
Coliform contaminations (including E. coli) are due to a fault in the treatment of wastewater. Their presence is a sign of a faecal contamination which makes the water unfit for consumption. If your drinking water system is fed by a well or a cistern, the risk is multiplied and calls for a high degree of vigilance.
How do I know if my water is contaminated?
Bacteria are invisible to the naked eye. The only way to reveal their presence is to perform a microbiological test on your water.
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.
Can my boiler which heats in real time be contaminated with legionella?
A boiler which heats in real time, i.e. without storing the water, does not constitute a risk.
However, if certain outlet points are far from the boiler, or are very little used, there is a danger due to the stagnation of water in these pipes. The stagnant water greatly promotes the creation of a biofilm on the walls of the system. This layer of organic depositions is very rich in nutrients and promotes the development of legionellae colonies.
After a long absence or period out of use, it is advisable to run the water for a number of minutes and to flush the circuit regulary at high temperature in order to detach the biofilm and remove a proportion of the bacteria. Make sure that you do not breathe close to the flushed-out water. However, it is possible that this flushing will eliminate only a superficial part of the biofilm and a proportion of the bacteria. This is why it is vital to regularly check the quality of the water at these specific points.
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.
I live in a multi-dwelling building. Is there a risk of legionella contamination?
The regulations compelling the providers of social housing and co-owners to carry out regular checks on the water systems is not the same from country-to-country. However, cases of legionellosis are constantly increasing throughout Europe and the United States. The countries which have legislated on this matter generally prescribe one obligatory test per year. This is entirely insufficient in the face of a risk which occurs throughout the year. In the event of positive contamination, the treatment will consist of a high-temperature thermal shock and a chemical shock based on biocide. Unfortunately, this may only destroy a proportion of the bacteria and of the biofilm, the layer of organic depositions from which the bacteria draw their nutrients. Recurrences are frequent unless more regular tests are carried out.
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.