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In these uncertain times, when fear of coronavirus is so prevalent, we are going to analyze the situation of swimming pools, their potential risks and the treatment that water must receive to ensure that the pool is a safe place.

The key question everyone asks is:

1. If the chlorination of the pool is carried out following the usual recommendations and applying the best practices, is it sufficient to deactivate the COVID-19 virus?

 And the second question is: 

2. Should users take any extra precautions that they did not take before?

Let's examine the SARS-CoV-2 virus...


Covid-19 is the respiratory disease caused by the SARS-CoV-2 virus, which we all know as Coronavirus. It is one of the seven coronaviruses that can infect people, such as SARS (Severe Acute Respiratory Syndrome) and MERS (Middle East Respiratory Syndrome) 4.

This family of viruses has similar physical and biochemical properties and comparable transmission routes.

The viral genetic material is enveloped in protein structures, called capsids. Viruses are divided into three groups depending on whether they are surrounded by an external lipid membrane (enveloped) or not (not enveloped) 5. The difficulty of removing the virus depends on the group to which they belong.

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Enveloped viruses are easier to eliminate: SARS-CoV-2, the virus responsible for COVID-19, is an enveloped virus and is therefore one of the easiest to eliminate.

According to the World Health Organization (WHO), a residual concentration of free chlorine of ≥0.5 mg / l in pool water for a minimum of 30 minutes of contact at a pH <8.0 is sufficient to kill enveloped viruses such as coronavirus 2 .

The following table shows some environments where the toughest viruses are disabled.

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Table: Virus deactivation. CDC (Centers for Disease Control and Prevention) 7


Diagram: Efficacy levels of disinfection by chlorine and UV light in the deactivation of various viruses 6.

The Diagram shows different levels of efficacy in deactivating various viruses and pathogens. Coxsackievirus, poliovirus, and rotavirus are examples of unenveloped viruses. It can be seen that they are deactivated with a Chlorine Ct of less than 15mg-min / liter. (The Ct value is the product of the concentration of a disinfectant (e.g. free chlorine) over the time of contact with the disinfected water.)

Therefore, an enveloped virus like COVID-19 would be in the green area of ​​the diagram and would deactivate even at lower Ct values.

As shown in the diagram, UV light disinfection widens the spectrum of efficacy considerably against other viruses.

Ultraviolet light has the ability to destroy the genome (DNA / RNA) of viruses, bacteria, and fungi, including coronaviruses. Standard disinfectants are effective against SARS-CoV-2, but as an extra level of protection, and / or to compensate for potential errors in the manual disinfection process, UV light can additionally be used to disinfect pool water once completed the chemical disinfection process. 8

Answer to Question 1: 

If pool chlorination is performed following current recommendations and applying best practices, is it sufficient to deactivate the COVID-19 virus?

Yes, in a conventional pool with a good hydraulic and filtration system that respects its maximum occupancy level, with a chlorine level of ≥0.5-1 mg / l throughout the pool, optimum water quality is achieved.

In other words, with a free chlorine level of ≥0.5-1 mg / l, the water is not only disinfected, but also has disinfecting potential to eliminate any virus or germ that may enter the water. 9

Pool automation is highly recommended for added peace of mind. (Otherwise, the responsibility for the health of the users falls entirely on the manager of the pool.)

Likewise, it is essential to regularly measure the main parameters (pH value and free chlorine level (DPD-1), either manually or automatically.

Residential pools and semi-public pools:

Chlorine tablets or liquid chlorine products can be used to obtain the proper level of free chlorine in the pool water. It is recommended to automate the dosing and control process. Another good alternative is to use saline electrolysis devices that automatically generate free chlorine from dissolved salt in the pool water.

To extend the disinfection spectrum, as an extra level of protection and to correct possible errors in the manual disinfection process, an ultraviolet (UV) light can be installed to disinfect pool water (in combination with dosed chlorine or saline chlorination) .

In semi-public pools, which tend to have a higher influx than residential pools, it is recommended to install an automation system, as well as online measurement of the main parameters with an intelligent pool analyzer.

Commercial pools for public use

To maximize safety, automation of the three phases is recommended: pH regulation (1), disinfection (2) and constant measurement (3).

(1) A correct regulation of the pH between 7.2 and 7.6 by means of acids or CO 2 is essential to guarantee effective disinfection.

(2) In order to broaden the disinfection spectrum, the use of ultraviolet light in combination with dosed chlorine (in tablets or liquid) or salt electrolysis is recommended.

(3) Constant measurement of pH and chlorine levels as well as automatic regulation of these parameters is essential in public swimming pools. Recommendation: Show the measurement results to the users, so that they are fully informed of the water quality.


Answer to Question 2: 

Should users take any extra precautions that they did not take before?

As in our daily life, we recommend maintaining adequate personal hygiene. For example, if there may be a risk of having touched surfaces, such as locker room benches, doors or knobs, it is recommended to wash your hands and / or sanitize them with disinfectant before entering the pool. We recommend bathers to always shower before and after swimming in the pool. It is also recommended to wash suits and bath towels, to eliminate all bacteria or viruses.

In addition to the pool water, it is recommended to keep the outdoor areas of the pool disinfected, as well as its equipment, such as showers, stairs, etc. applying products specially indicated for this use.


1.   Guidelines for drinking water quality, fourth edition, which incorporates the first addendum. Geneva, World Health Organization; 2017 ( 789241549950-eng.pdf, accessed March 3, 2020 )

2.   Water, sanitation, hygiene and waste management for COVID-19. Technical report. March 19, 2020. ( )

3.   PWTAG Pool Water Code of Practice - 2016 Updated to reflect Pool Health and Safety Management Requirements (HSG179)

4. accessed March 2, 2020

5.   How to choose effective disinfectants against the coronavirus that causes COVID-19. ( disinfectants-use-against-novel-virus-covid-19) (accessed March 2, 2020 )

6.   Environmental Protection Agency's Manual for Water Treatment and Disinfection Guide, 2011. ( )

7.   Effects of chlorination on the deactivation of the selected pathogen. U.S. Centers for Disease Control and Prevention ( )

8.   About UV disinfection. ( )

9.   On the hydrogen peroxide, known as liquid active oxygen, in the pool market ( ): “H2O2 in a concentration of 3% deactivated all Study virus within 1 to 30 minutes. The viruses causing the Coronavirus and the flu turned out to be the most sensitive. Reoviruses, adenoviruses, and adeno-associated viruses were relatively stable. The H2O2 is an effective means for deactivating the virus. “Recommended concentration in pool water: 10 - 30 ppm H2O2.

Potassium monopersulfate, known as solid active oxygen for swimming pools, respecting the recommended concentration of 5 - 10 ppm KMPS in water, is also effective against the virus. ( )

Bromine in its different forms (Br2, BrCl, HOBr-) is used in swimming pools and spas (Jacuzzi). Bromine has been used to deactivate bacteria, viruses and protozoa in various laboratory studies on disinfection (Kim, 2014). ( ) Recommended residual levels: 1-3 ppm in residential pools; 3-5 ppm in residential spas.


Other references:

Guidelines for safe environments in recreational waters. Volume 2. Pools and similar environments. WHO publication, 2006. ( )

APRIL 2020

Water Quality for Engineering & Trade is distributor for Astral Spain swimming pool products

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