A PROPERLY TREATED SWIMMING POOL IS A SAFE PLACE.
Zodiac's mission is to assure a perfect pool experience for all the users, in residential swimming pools, in semi-public commercial pools (communities) and publicly used commercial pools.
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 we’ve been asked are:
1. If my 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 my pool sanitised?
3. Should I be doing anything differently to the pool compared to what I’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.
The diagram 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.
If my swimming pool is chlorinated according to current best practices and recommendations (Free Chlorine: 1.0-3.0ppm), is this sufficient to inactivate COVID-19 virus?
Yes, for a conventional swimming pool with good hydraulics and filtration, operating within its design bathing load, adequate water quality is achieved with a free chlorine level of ≥0.5-1.0ppm throughout the pool. Lower free chlorine concentrations (0.5 ppm or less) will be adequate when chlorine is used in combination with ozone or UV disinfection.
This means: with a free chlorine level of ≥0.5-1 mg/l the water is not only crystal clear and disinfected, it also has the ability to tackle any virus or pathogens which may be taken into the water.
What’s the best way to keep my pool sanitised?
Routine measurement of the main water quality parameters is essential. It is recommended to regularly check the pH, Free Chlorine and Total Chlorine either by test strips and test kits, or through a specialist poolcare retailer or service business provider that can complete a full diagnosis. Testing for other parameters such as Total Alkalinity (buffer), Hardness, Cyanuric acid (stabiliser), metals and phosphates will help keep the pool and pool equipment in a good condition.
Residential pools and semi-public pools:
The correct level of free chlorine in the water can be reached by dosing solid chlorine (granular or tablets) or liquid chlorine. Automation of this dosing & regulation process is possible and highly recommended for ease of mind. Another alternative is to use a Salt Water Chlorinator to automatically generate active free chlorine from salt dissolved in the water.
For an extra level of protection, and to shield against possible errors in the disinfection process, ultraviolet light (UV) can be installed to disinfect pool water (in combination with either chlorine dosing or salt chlorination).
Automation is highly recommended in semi-public pools, which will generally have a higher bather load than residential pools. New products such as smart pool analyzers can also automatically measure main water quality parameters and share them online for continual remote monitoring.
Public commercial pools:
To maximise safety, the recommendation is an automation of all three steps: the pH-value regulation (1), the disinfection (2) and the continuous measurement (3).
1. A correct pH value regulation between 7.2 and 7.6 with acids or by means of CO2 will be essential to guarantee the effectiveness of disinfection.
2. To amplify the spectrum of disinfection, the use of UV is highly recommended in combination with either chlorine dosing or salt chlorination.
3. Continuous measurement of pH and chlorine levels and an automatic regulation of these parameters is highly recommended in public pools. Recommendation: Display the test results to swimmers, so they are fully informed about the water’s quality.
Depending on the bather load and availability of automation on the pool, testing frequency will vary from state to state in Australia. Consult your local legislation for testing requirements.
Should I be doing anything differently at the pool compared to what I’ve been doing before?
Yes, a very important thing to remember before dipping into the pool is proper personal hygiene, especially when everyone is at risk from just touching various surfaces like the changing benches, doors, and handles.
a) Handwashing will always do the trick: properly and thoroughly washing your hands for at least 20 seconds with soap and water and/or disinfect your hands before entering the pool.
b) Shower before and after swimming in the pool.
c) After visiting a public pool, remember to wash and maintain clean swimming kits and towels by using at least a high 60-degree wash to kill any bugs or bacteria.
Apart from maintaining the pool water quality, it is recommended to keep surrounding areas and equipment like showers, ladders, pool deck, etc. disinfected by applying appropriate sanitisers.