Coronavirus: Proper chlorination stops water transmission, HSE advises

Coronavirus cannot be transmitted in drinking water and swimming pools so long as they are properly chlorinated, the Health Service Executive has advised.

Adherence to current recommended disinfection practice is sufficient to “inactivate” the Covid-19 virus in chlorinated drinking water and swimming pools, according to advice note prepared by the HSE to address concerns on the issue.

Chlorination is the most commonly used method of water treatment in Ireland for both drinking water and swimming pools.

The HSE says it has a "long history" of preventing waterborne illness, with the World Health Organisation recommending specific concentrations of chlorine in drinking water, as well as specific "contact time" needed to ensure dangerous germs are killed.

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There are three difference groups of viruses: enveloped viruses, surrounded by an outer lipid membrane; and large and small non-enveloped viruses, which lack this membrane.

Easier to kill

According to the advice note, enveloped viruses are easier to kill than non-enveloped viruses: “Sars-CoV-2, the virus responsible for the Covid-19 outbreak, is an enveloped virus and therefore the easiest to kill of the three types of viruses”.

The World Health Organisation recommended chlorination level of 15mg.min/litre is sufficient to kill non-enveloped viruses such as poliovirus, rotavirus and coxsackievirus, and an enveloped virus such as Covid-19 would be inactivated at even lower levels, the document says.

The same rationale applies to standards used to control microbiological hazards in swimming pools treated with disinfectant, it says, although the amount of chlorine required varies according to the type of pool or chlorination chemical used. Jacuzzis or other types of spa pools may need a higher amount, for example.

Of all the organisms that threaten the purity of water supplies and swimming pools, cryptosporidium requires the highest dose of chlorine to be inactivated.