“Infinitesimal traces” of SARS-CoV-2 were found in the city’s non-potable water network, which is primarily used to clean the streets and water public gardens, it said.

The traces were found “in the last 48 hours” in four samples of 27 taken from the water by municipal authority Eau de Paris, led by the Mairie. This water source was immediately suspended from use “as a precaution”, the Mairie said.

Drinking water for the city comes from another “totally separate” water network, which itself “has no trace of the virus”, and “can be consumed with no risk”, the Mairie confirmed.

Paris has two independent water networks, which separate drinking water from non-drinking water, as a legacy of systems dating back to the 19th century.

The Mairie said: “The non-potable water network is fed by what we might call ‘raw’ water, from the Seine and the Ourcq canal, and is not given intensive treatment.”

It is used to water some parks and gardens, to clean the streets, to feed lakes and certain waterfalls in city parks and wooded areas, and is also used for “some ornamental fountains in parks and gardens that are currently closed to the public”.

Célia Blauel, environment deputy mayor of Paris, said: “These are infinitesimal traces, but traces regardless. So we have decided to take precautions, and consult the [regional healthcare agency] l’Agence Régionale de Santé (ARS), so they can analyse if there are any potential risks.

“As we have an internal laboratory, we were the first to get these results, and to sound the alarm.”

Karine Lacombe, head of infectious diseases at the Saint-Antoine hospital in Paris, told Le Monde newspaper: “[Even] though we know that [the virus] contains genetic material, we know that the virus cannot spread in the environment, because it needs human cells, and to attach onto to enzymes of human cells to multiply.

“So I am quite reassured on the issue of whether this virus can be transmitted [through water].”

According to the World Health Organization (WHO), it is not technically impossible that the virus could be transmitted through water, but in mid-March it said that there was currently no proof that it could be transmitted through drinking water or other water sources.

Studies of similar viruses show that they can survive for two days in non-chlorinated water at 20°C. The WHO has consistently said that the risk of SARS-CoV-2 contamination from drinking water systems is "low".

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