Transparency and the precautionary principle. This Sunday afternoon, the City of Paris revealed, in a press release, the presence "in minute quantities" of traces of the Covid-19 virus in its non-potable water network. This water is mainly used for street cleaning.
The drinking water network, on the contrary, is completely independent, and constantly monitored. It feeds both household taps and public drinking fountains. This drinking water is subjected to so-called multi-barrier treatments, which make it possible to eliminate all traces of pollution, and in particular any virus. So no danger for water drinkers, reassures the City.
Following the results provided by the Eau de Paris laboratory (the public operator in charge of the production and distribution of water in the capital), the City immediately contacted the Regional Health Agency to analyze the possible risks presented by these traces in non-potable water, the use of which was immediately discontinued.
However, many questions arise.
1. Is the presence of the virus in the non-potable water network a surprise for Parisian specialists?
"This is not entirely a surprise," points out Célia Blauel, assistant to the mayor of Paris in charge of water. In a crisis situation, we are more vigilant about the quality of water. ” “The presence of various viruses in this wastewater is usual and classic during epidemics such as gastro or flu. There was no reason why the Covid should escape it, ”adds Laurent Moulin, microbiologist in the laboratory of Eau de Paris.
"On the other hand, we did not expect to find it in non-potable water networks after the first level of sanitation", however specifies Célia Blauel.
2. Is there a risk to the drinking water network?
"There is no risk for the drinking water network, drunk from the tap," insists and insists Emmanuel Grégoire, first deputy to the mayor of Paris. This drinking water is in fact the subject of “multi-barrier” treatments with ultraviolet, ozone and chlorine.
"Paris is fortunate to have two very distinct networks: that of drinking water with its 2,000 km of pipes, and the non-drinking water network, of 1,800 km, which comes from the Second Empire, and which normally allows us to clean the streets of Paris and water the gardens of the capital. ”
3. What are the origins of these traces?
“The origin is completely natural. It comes from water flowing from the toilet after the excrement and urine of the sick. They are widely combated in treatment plants. But this non-potable water, known as raw water, is still found, after treatment, in the natural environment, the Seine or the Ourcq canal, ”explains Célia Blauel.
4. So the Seine and the water from the Ourcq canal are infected?
"Yes, since we find traces of it in the non-potable water which is collected directly in the Seine, pumped at the Austerlitz factory or under the rotunda in the 19th century for the Bassin de la Villette. It is therefore even more inadvisable to swim in the Seine at the moment, ”specifies Célia Blauel. Even if the contamination is done mainly by respiratory way.
5. When and where was this virus detected?
“The first results of infections were found at the end of last week. The water quality monitoring program revealed the presence in trace quantities of traces of the virus on 4 of the 27 sampling points tested, randomly, at the exit of the supply outlets of the trucks cleaning the streets of Paris ” .
6. What does this “infinitesimal” presence represent?
"It's true, we have been looking for the little beast," recognizes Laurent Moulin. And they found ... "So in untreated wastewater, that rate rises to a million genome units. Once treated, this represents only 1,000 genome units per liter. So there are 2,000 to 5,000 times less virus in the non-potable network than in wastewater. ” The numbers seem huge. But these traces are so weak that non-potable water could continue to be used, as long as there is no aerosolization, says Laurent Moulin.
7. Which laboratory has detected this presence of the virus?
This laboratory located in Ivry-sur-Seine has a running water analysis service, but also a research and development laboratory, precisely specialized in the research of viruses. This specialty was introduced in 2010 and has been reinforced with the risks of scientific terrorism.
8. What is this non-potable water used for?
It provides water for watering certain parks and gardens, cleaning streets and operating lakes and waterfalls in parks and woods, as well as certain ornamental fountains in parks or gardens currently closed to the public.
9. What are the concrete consequences in Paris today?
“Last week again, from the 150 filling points of the cleaning trucks (which use 500 m 3 per day of non-potable water), our services cleaned the streets of Paris with big water. The usual use of this non-potable water was stopped this Sunday, "says Paul Simondon, deputy mayor of Paris in charge of cleanliness.
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“The cleaners worked in protected clothes, with masks, gloves, boots and glasses. Now the streets are cleaned with potable water. Watering the lawns of parks and gardens, on the other hand, is suspended. "
10. Who will make the decision to return to normal?
"We will await the detailed opinion of the High Council of Public Health and the decision of the mayor of Paris," says Emmanuel Grégoire.
20% less drinking water consumption
It is a side effect of the Covid-19 crisis. "We note a 20% drop in water consumption in Paris since the start of confinement," notes Célia Blauel, assistant to the mayor of Paris in charge of water.
Average daily consumption is around 480,000 m3 to 500,000 m3 of water per day. And it has fallen to 400,000 in recent weeks ... Explanation? The departure of Parisians who fled the capital. The absence of tourists. The absence also of all office workers who stayed at home in the suburbs.
But it is above all the brake on economic activity which cut the flow of water, knowing that for 2 liters of bus by a Parisian, consumption revolves around 130 liters per inhabitant (on average) because of all other activities. Today, it is all the usual consumption of restaurants, bistros and hotels that have been put into forced shutdown, as well as that of hairdressing salons, which has had an impact on Eau de Paris meters.
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