Are pools safe during Covid-19?


In these times of uncertainty and fear of coronavirus on peoples’ minds, let’s have a look at swimming pools, their potential risks and the necessary water treatment required to make the pool a safe place to swim.

The main questions to ask are:

1. If a swimming pool is chlorinated according to current best practices and recommendations (Free Chlorine: 1-3ppm), is this sufficient to inactivate COVID-19 virus?

2. What’s the best way to keep a pool sanitised?

3. Should we be doing anything differently to the pool compared to what we’ve been doing before?

COVID-19 is the respiratory illness caused by the virus SARS-CoV-2, that we all call Coronavirus. It is just one of the seven coronaviruses that can infect human beings, like SARS (Severe Acute Respiratory Syndrome Coronavirus) and MERS (Middle East Respiratory Syndrome Coronavirus) 1. This family of viruses have similar physical and biochemical properties and comparable transmission routes. Virus genetic material is packaged inside protein structures called capsids. Viruses are divided into three groups depending on if they are surrounded by a small or large outer lipid membrane (enveloped) or no membrane (non-enveloped). Depending on their group, the difficulty to kill them varies. Enveloped viruses are easier to kill: SARS-CoV-2, the virus responsible for the COVID-19 outbreak, is an enveloped virus and therefore the easiest to kill. The World Health Organisation (WHO) states that a residual concentration of free chlorine of ≥0.5 mg/l in the pool water after at least 30 minutes of contact time at a pH <8.0 is sufficient to kill enveloped viruses like coronaviruses.

Diagram: Efficacy levels of chlorination and UV in the inactivation of various viruses (EPA).


The diagram above shows the level of chlorine and length of contact time required to inactivate different viruses and pathogens. The most difficult to kill viruses such as Coxsackievirus, Poliovirus and Rotavirus (non-enveloped viruses) are inactivated at chlorine Ct* of less than 15mg-min/litre. (This means that they are killed when there is 1ppm free chlorine in the water for 15 minutes or when there is 3ppm free chlorine in the water for 5 minutes).

*A Ct value is the product of the concentration of a disinfectant (e.g. chlorine) and the contact time with the water being disinfected.

Therefore an enveloped virus such as the COVID-19 virus, that is easier to kill, would be situated in the green area of the diagram and will be inactivated at even lower Ct values.

At Swimz we use a Salt Water Chlorinator to automatically generate active free chlorine from salt dissolved in the water.


The diagram above also shows how UV disinfection can be used to amplify the disinfection efficacy considerably against other viruses and pathogens. Ultraviolet light has the ability to destroy DNA of viruses, bacteria, and fungi, including coronaviruses. Standard disinfectants are effective against SARS-CoV-2 but as an extra level of protection where there are drops in sanitisers (e.g. heavy bather load), ultraviolet light can be used to disinfect pool water after the chemical disinfection process is completed.

At Swimz we have installed an industrial strength medium pressure UV unit, imported from Netherlands for your added safety (