Clearing up a cloudy issue concerning pool water

by Sally Bouorm | August 1, 2013 3:17 pm

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By Dr. Jeff Williams and Nathan Kenney

A report by the Centers for Disease Control and Prevention (CDC) earlier this year entitled “Microbes in Pool Filter Backwash,” stirred up mass media attention, creating a cloud over public perceptions of swimming pool safety just as the season was entering full swing. In particular, reminding bathers about personal hygiene as a component of public pool use is always a good thing; however, the report’s findings rapidly became sensationalized by content-hungry news channels.

Rather than focusing public attention to the behavioural changes the CDC strives to attain, the report, which comprises an unsurprising set of microbiological findings on a limited range of pool filter samples, was converted from what should have been a general news story into lurid coverage of “poop in pools everywhere.”

This is unfortunate because making a beneficial and wholesome activity such as swimming more attractive to the masses, and encouraging increased participation, is critical to the efforts of getting people off the couch and doing something healthful, yet delightful. Raising fears about recreational water illness (RWI) risks can be a setback to these efforts. Therefore, it is important to use data from studies such as these in a healthier perspective.

Interpreting the ‘high-tech’ findings and assessing the risk

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For this study, CDC researchers collected 161 backwashed pool filter samples from a number of public swimming pools, and tested them for biological contaminants using DNA probes. For this procedure, filtered particulates ended up being highly concentrated in a small amount of backwash water, which was then analyzed using DNA ‘fingerprinting’ to detect whatever was trapped on the filter medium. Due to the extraordinary sensitivity of this procedure, many of the filters, which were performing properly, were sure enough found to have trapped bacteria to the extent that more than half of the samples showed evidence of the presence of Escherichia coli (E. coli), which is commonly used as an indicator of fecal contamination. Roughly the same proportion also contained ‘fingerprints’ of Pseudomonas aeruginosa (P. aeruginosa), a microbe that can be human-associated, sometimes causing disease, but which can occupy and multiply in a wide range of environmental niches.

Now, what these findings signify has to be framed by the limitations of the technology; DNA probes provide quick and sensitive ID analysis of samples for specific microbes, but the interpretation of the results is limited without using other types of microbiological tools to arrive at an assessment of RWI risks. For example, the DNA technology used in the study will provide a positive signal in the backwash water sample whether the microbe is alive and potentially infectious, or dead and harmless—in this instance most likely eradicated by the pool’s chlorine (Cl) sanitizer, which is doing its job, taking care of the inevitable microbial contamination as a result of the pool’s bather loads. It would have taken many more microbiological procedures to get a handle on whether the E. coli or P. aeruginosa fingerprints truly represented a RWI risk, thus signifying the sanitation/filtration systems were faulty or not properly maintained. These are the types of signals that should cause alarm; however, they are often discovered in the aftermath of disease outbreaks.

That said, there were no such outbreaks at the pools involved in the study, thus, the findings, which garnered widespread attention, were not indicators of wholesale failures of proper sanitation and hygiene, and the bacteria detected were not in the primary disease agent category (e.g. E. coli O157;H7). Therefore, all of the anxieties raised by the newspaper headlines were not necessarily in good cause. Safe pool management practices were clearly working.

Adopting good personal hygiene practices as a way to lessen the amount of contamination the pool’s sanitation/filtration system has to deal with is a fair proposition; however, it is yet to be determined whether showering before entering the pool would significantly reduce the rate at which ultra-sensitive DNA probing returns positive signals of human-related microbial material in filter backwashes. It is certainly a reasonable notion, but it will be a challenge to test experimentally.

Chlorine: Upside/downside

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Significant, but almost lost in the high visibility of this report, was the detection in some samples of parasite cyst fingerprints. In these instances, even the best chlorine sanitizing system is not capable of inactivating Cryptosporidium (Crypto) oocysts. These samples are more likely to have a human feces origin in the pool water, and almost certainly would still be alive and infectious in the filter. Of course, filtering them out and regularly backwashing into the septic outflow is another component of ongoing effective pool management; however, in these cases, there is a higher risk to bathers and there is much less certainty with respect to the filter medium’s ability to capture and eventually remove oocysts as these microbes measure only a few microns (µm), and, therefore, are able to pass through the pore tunnels of commonly used filter media beds.

These microbes are a real RWI hazard and one with explosive potential as they are highly infectious. In serious cases, a large pool with enough chlorine-resistant cysts is likely to ensure a mouthful of water would contain an infectious dose. With this in mind, there is good reason to take the presence of Crypto in backwash samples, even at a low rate (the CDC study found Crypto oocysts in less than two per cent of the samples) as a serious indicator of potential problems.

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This risk is not readily diminished by adopting sanitizing alternatives to chlorine. For all its downsides, including objectionable smell, taste, eye and skin irritation, and disinfection byproduct generation, amongst others, chlorine serves up an unmatched array of advantages in maintaining safe pool water, and is deserving of its centrepiece role in recreational water sanitation. The fact chlorine does not cope with the toughness of Crypto oocysts, in addition to some other shortcomings, has led the industry to look for alternatives. However, this has not proven easy, and while practical alternatives are available, they bring their own weaknesses to the challenge. Chemical agents with oocyst-inactivating power such as chlorine dioxide (ClO₂) and ozone (O₃) pose more operational demands on users than chlorine, and cannot compare in their inability to sustain biocidal activity in the main body of pool water that is readily accomplished with chlorine residuals.

Ultraviolet (UV) irradiation can destroy the infectivity of oocysts; however, it too does not offer any residual protection to the recirculating water and it must operate via line-of-sight exposure to the inactivating rays. Any obstruction in the form of turbidity in pools with heavy bather loads can undermine the advantages of UV. Further, its inactivating power must wait upon the arrival of germs over the course of the pool’s turnover; in the meantime, they are free to wreak havoc.

Clearer is safer

This leads to the final piece of the framework for this perspective on the CDC report—water clarity as a contributor to pool water safety, regardless of the method of disinfection being deployed.

Turbidity is the enemy of effective water safety management and efficient filtration is the way to counter it. Turbidity interferes with UV, consumes disinfectants (i.e. its ‘demand’ for halogen [e.g. chlorine, bromine (Br), etc.], meaning less is available for sanitation), and it contributes to the risk of drowning by obscuring the view of bathers who get into trouble and sink out of sight.

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Filter backwashes should contain evidence for what the medium is removing from the water—just as CDC researchers found—but helping that process by flocculating suspended particles is a worthy goal, and it can be achieved as a part of regular pool management. By using a natural biopolymer[6] formulation, specifically aimed at improving filtration efficiency, Crypto oocysts and other microbes become enmeshed in large floccs (shown in Figure 1). This allows pool filters to more readily trap these microbes, reducing the chance they remain in the recirculating body of water and cause RWI outbreaks. With this method of treatment, microbes as small as 2 µm long and 0.5 µm in diameter can be aggregated into clumps (shown in Figure 2), which end up being trapped by, in this case, a flat filter membrane with 5 µm pores; without treatment, these microbes simply pass through the filter. Then, proper pool sanitation can be counted on to inactivate most other disease-causing agents.

This treatment is also effective at trapping other waterborne microbes (e.g. Giardia, E. coli), in addition to algae. For large pools, polymer treatments can be accomplished via controlled metering, while manual treatments, at properly timed intervals, are also practical for smaller scale operations. The polymers used in this treatment are biodegradable and safe for bather exposure, and the concentrations required are extremely low (typically in the range of parts per billion [ppb]).

BATHER LOAD BACTERIAL SLOUGHING EXPLANATION

[7] Whenever a person swims in a pool, bacterium and viruses from their skin and hair (not to mention any incontinent accidents) are left behind and the vast majority of these microbes will be eradicated by the chlorine (Cl) in the pool. The bacteria, which live on the skin of healthy people, are not necessarily harmful unless the person already has lowered immune defenses. Those who typically fall into this category include young children, seniors, pregnant women, AIDS patients, and those on immunosuppressant medication. It is not unusual for DNA probes of swimming pool filters to find bacteria as common as P. aeruginosa or Escherichia coli (E. coli) given the former lives on most surfaces in civilization, while the latter is present in microscopic amounts on everything one would touch after going to the washroom. It should also be made clear that there is a small sub-group of E. coli that is responsible for severe illness, resulting in vomiting and diarrhea, called E. coli O157:H7. These bacteria make people sick, and, if found in a pool filter, it would indicate a swimmer(s) was sick with the above symptoms when they went swimming. Almost any other E. coli contamination would simply indicate swimmers were not cleaning themselves thoroughly before using the pool, and while this is unsanitary, it is not a cause for alarm if the pool is properly chlorinated and maintained. Knowing the difference between each strain, it can be considered that the Centers for Disease Control and Prevention (CDC) report on “Microbes in Pool Filter Backwash,” did not find any traces of E. coli O157:H7 with the DNA probe, but did find other non-specific E. coli. This shows the contamination in most pool filter samples was the result of dirty swimmers—not because severely sick people contaminated the entire pool, thus making it dangerous for all other swimmers. Further, in the case of either E. coli strain, chlorine will kill whatever is floating in the pool as long as the sanitizer levels are kept appropriately high. Proper chlorine use is vital to keeping pool water clean, safe, and free of infectious microbial contaminants.

Use all the tools available

Encouraging a multipronged approach to pool water sanitation, with proper attention to disinfection, clarification, and filtration, as well as emphasizing the role of personal hygiene measures for all bathers, will likely lead to more enjoyable recreational water experiences. Properly implemented, these pool water management practices work; the aquatics industry strives to achieve the safest environment and this is how it should be perceived.

 

 

Dr. Jeff Williams is the chief technology officer and senior vice-president of R & D for Halosource Inc., a clean water technology company based in Bothell, Wash. He is an emeritus professor of microbiology and molecular genetics at Michigan State University, where he was a teacher and biomedical researcher for almost 30 years before founding Halosource in 1998. Williams can be reached via e-mail at jwilliams@halosource.com[8].

 

 

Nathan Kenney is a water microbiology specialist for Halosource’s product development division. He joined the company in 2012 and is involved in development and testing. He received his bachelor of science (B.Sc.) in microbiology from the University of Washington. He can be reached via e-mail at nkenney@halosource.com[9].

 

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