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Clients have been calling recently with concerns about COVID-19 and worries about virus transmission through pools and other bodies of recreational water.

I’ve also been hearing from members of the general public who perceive some pools, particularly spas, wading pools, waterpark activity pools operating above maximum capacity, and spraygrounds as giant germ incubators.

Some pools with extremely high bather-load-to-water-volume ratios, and some venues (cruise ship spas, for example) do cause me to worry that guests are contracting recreational water illnesses from using these pools. Health regulators are reporting a record number of public pools and spas failing their routine inspections and being closed due to inadequate water chemistry or water quality. We know that there are pools being operated by pool technicians without adequate training in water chemistry and proper maintenance practices. We know some pool operators are following out-of-date maintenance and clean-up procedures because they are simply unaware of current industry standards and practices.

The good news is that we do know how to prevent the spread of recreational water illness, most large public pool and waterpark operators are trained professionals and do know what they are doing, and thankfully, the coronavirus does not transmit through pool water.


The coronavirus, like all viruses, is not a living organism. It cannot be killed – it decays. It is a single-strand ribonucleic acid (RNA) linear protein molecule (as compared to double stranded DNA) covered with a protective layer of nonpolar, hydrophobic lipids (fats) that do not dissolve in water. The virus mutates and multiplies when absorbed into the mucous membranes of your eyes, nose, or mouth. But this is actually difficult to do because the function of the mucosa is to prevent dehydration of these bodily tissues and stop dirt and pathogens from entering the body.

The virus is more concentrated in confined spaces and needs moisture and darkness to stay stable. It is more durable in cold or air-conditioned indoor spaces, and is more likely degrade in dry, warm, bright, dehumidified environments. It is not a living organism like bacteria or protozoa, so a bactericide will not kill it –- you can’t kill something that is not alive. But, soap and detergent foams will dissolve the protective external fat / lipid layer, as will heat above 77° Fahrenheit, and ethyl alcohol with a greater than 70% concentration.

Chlorine compounds, hydrogen peroxide, ozone, and ultraviolet light, particularly UVC, can be used to degrade or dissolve the RNA protein molecule. A solution of one part household bleach (Clorox) to five parts water will dissolve the RNA protein molecule from the inside. The World Health Organization (WHO) currently recommends using sodium hypochlorite at 0.5% / 5,000 ppm / 1:200 for disinfecting surfaces (1% equals10,000 ppm).

The Centers for Disease Control and Prevention (CDC) recommends that a freshly diluted 5.25-6.15% household bleach hypochlorite solution at a ratio of 1:100 be applied to an already cleaned surface to disinfect after small spills. Or mix a 1:200 solution if utilizing 10-12% commercial grade sodium hypochlorite (liquid pool chlorine). For large spills, use a 1:10 ratio followed by a 1:100 solution of household bleach, or 1:20 then 1:200 commercial sodium hypochlorite solution to disinfect, then let air dry. Typically, a 1 to 10-minute contact time is recommended.

Cleaning and Routine Maintenance

Although there have been no cases of COVID-19 transmitted through pool water, the virus could certainly be present in the air or on surface at an aquatic facility. And many other diseases do transmit though pool water. Pool operators should develop Standard Operating Procedures (SOP) to immediately destroy germs in pool water, in the air or on surrounding surfaces, and prevent harmful bacteria, amoeba, and protozoa like Pseudomonas aeruginosa, MRSA, Legionella, Naegleria fowleri, or Cryptosporidium, from causing disease.

Aquatics facilities should have a written chemical treatment, cleaning and routine maintenance plan to prevent pathogens from being a problem in the first place. Checklists should be completed on a daily basis, and items checked-off by the person who actually completed the task, and only after a task is completed. The checklist should be reviewed by a supervisor. After inspection to verify satisfactory completion, the supervisor should sign the checklist indicating the facility is operational ready.

The facility should be spotless. Tidy up. Pick-up and dispose of trash, move items left by patrons to the lost-and-found, and return any items that don’t belong there to where they belong.

Next, clean the facility. Cleaning means to physically eliminate dirt, debris, spills, soiled areas, organic (living fats, lipids, proteins, enzymes) and inorganic (non-living salts, elemental compounds and solids) matter. It is necessary to clean before disinfecting, because some germs may be hidden or protected by residue (for example bacteria being harbored by algae or slimy biofilms, or viruses by lipids).

Clean using friction and soap and water, detergents, enzymes, or trisodium phosphate (TSP). Or instead clean mechanically by using a machine like a power scrubber or pressure washer. Soaps are produced from natural ingredients like fats and oils from plants. Detergents are synthetic, man-made cleaning products that mix with dirt and other impurities to make them better able to dissolve in water. Scum or insoluble precipitates don’t form when detergents combine with salts and minerals in hard water when detergents are used instead of soap. TSP used to be added to most detergents to soften the water and make them foam better, but has been removed by manufacturers from many products in recent years due to wastewater environmental impact concerns (algae growth and reduced oxygen levels in lake water). As a result, our dishes and laundry are not as clean. However, TSP is still widely available as a stand-alone product and is commonly used for cleaning in aquatic facilities. Use a diluted 1:20 solution for general cleaning, and 1:10 ratio for stubborn stains. With all cleaning products, apply, soak, scrub, then rinse thoroughly to remove the cleaner residue so it doesn’t interfere with disinfection.

After cleaning, then disinfect. Disinfection kills or inactivates pathogens (disease causing organisms). Disinfection is not the same as sterilization. Sterilization kills or eliminates all biological organisms – harmful or beneficial, by physical or chemical means. When disinfection inactivates a pathogen, the replication and spread of the germ is prevented. Steam will disinfect, as will alcohol, many commercially available disinfectant products, biocides, chlorine compounds and other halogens, ozone, and ultraviolet light (particularly UVC).

Don’t forget to clean and disinfect both vertical and horizontal surfaces. In addition to floors, decks and walls, make sure to include benches and all seating, rides and attraction surfaces, slide transport media (inner tubes, rafts, mats), wet suits, goggles, masks, fins and snorkels; racing lane lines, rescue equipment like back boards and rescue tubes, kickboards, instructional equipment, any items shared by staff or used by more than one patron.

When the cleaning and disinfecting process is completed, launder or properly disinfect cleaning equipment like brushes, brooms, buckets, skimmer nets, towels and rags before they are put away.

A few reminders

Check to be sure products used for cleaning and disinfecting are compatible with pool water and do not create any unwanted side effects. Do not permit employees to come to work when they are sick. Make sure employees wear appropriate personal protective gear (PPG). Read the EPA label on the product and the Safety Data Sheets (SDS) to determine what PPG (neoprene gloves, boots, splash guard aprons, goggles or full-face shields, SCBAs) should be worn while handling chemicals. Review your staff training documents to be sure employees have Pesticide Worker Safety Training, and OSHA required Hazardous Materials training before handing and using cleaning and disinfecting products. Follow the manufacturer’s instructions on storage, disposal, dilution, spill containment and compatibility.

To ensure that disease is not transmitting through the water itself, follow industry standard operating procedures for continuous circulation, appropriate flow rates and turnover times given the type of pool and bather load, sizing of filters, and backwashing, cleaning, inspection and replacement of filter media or elements. Maintain adequate sanitizer residuals, and keep the ORP set point at 750 mV or above. Keep the water balanced. Install a secondary ozone or UV light water treatment system – many emerging pathogens are resistant to chlorine at the levels typically maintained in pool water during normal use. Do not use isocyanurates as your primary sanitizer-oxidizer, and do not add cyanuric acid to non-stabilized chlorine compounds. Although it has some benefits in preventing loss of chlorine due to exposure to sunlight, cyanuric acid ties up the hypochlorous acid, significantly slows down the sanitation process and reduces the oxidation reduction potential.

Perform regular bacteriological water analysis. Collect water samples and take swabs (inside filter tanks, hair and lint filters, skimmers, at the waterline, on the deck, in the locker rooms…). Have the samples analyzed by an independent laboratory for indicator bacteria like fecal Coliforms, E. coli, and Pseudomonas aeruginosa. Review the results. If results are positive, try to identify the source of contamination, and follow CDC decontamination procedures if necessary.

Address the issue of biofilms. CDC claims an estimated 65% of disease transmission through pool water and the resulting recreational water illness can be traced to the build-up of biofilms in pool piping and equipment. Dismantle and clean and disinfect surfaces where accessible. Inspect pipes and difficult to reach components using illuminated, waterproof video and flexible cable. Consider designing new circulation systems to allow pigging or manual scouring of pipes. Begin using biocides that are effective at destroying the biofilms that harbor and organize pathogenic organisms.

It’s also a good time to review and possibly revise procedures which promote healthy swimming and help prevent disease transmission at your aquatic facility. Update policies concerning the use of pools by non-toilet trained children, whether and what type of swim diapers will be permitted, where diaper changing will be permitted, and instituting regular bathroom breaks. Make sure your blood, vomit, dead animal, and fecal incident clean-up procedures are consistent with current CDC recommendations. Post signs prohibiting patrons who have open wounds, contagious diseases, or who have had active diarrhea within the past 14 days from using the pool.

For closed pools

Also if your pool is temporarily closed down due to the pandemic, don’t just shut off the circulation system and walk away from the facility. You don’t want the water to turn into a swamp, start attracting mosquitos and wildlife, and become a safety and public health hazard. Don’t empty the pool of water either. What keeps a pool in the ground is the weight of the water, not the weight of the pool structure itself. Draining a pool may result in extremely expensive hydrostatic damage. Instead, make sure barriers are intact and the facility is properly secured, safety covers are installed, and security measures are in place to prevent vandalism or unauthorized entry onto the premises. Turn off the heater. Brush down the walls, skim out any floating debris, vacuum the pool, and backwash the filters. Add algaecides and chelating agents to prevent mineral staining and the growth of algae. Put the pool into idling mode. Cycle the circulation system on and off. Cut back from continuous 24 hour circulation, but try to get at least one complete turnover of water per day. Continue to chemically treat the water. Visually inspect the pool regularly, test the water and make sure that water quality is not deteriorating. If you idle properly, you should be able to get back into operation quickly and after only a few days of normal circulation and bringing water quality back up to operating standards.