Pseudomonas aeruginosa and Water Disinfection: Lessons from Drinking Water and Swimming Pools
Keeping water microbiologically safe is not simply a matter of treating it once and assuming the problem is solved. Different water systems face different sources of contamination, operating conditions, and treatment challenges. Pseudomonas aeruginosa is a useful example. Pseudomonas aeruginosa is a clinically significant multidrug‑resistant pathogen. Widely distributed in nature, it possesses intrinsic robust antibiotic‑resistance mechanisms and is linked to multiple severe illnesses. It can cause hospital‑acquired infections including ventilator‑associated pneumonia and various septic syndromes. The WHO lists Pseudomonas aeruginosa among the pathogens posing the greatest threat to humans due to antibiotic
A 2021 study by Vukić Lušić et al. analyzed 9,230 drinking water and swimming pool water samples collected in Croatia between 2016 and 2020, offering useful insights into where P. aeruginosa occurs and what these findings may mean for water disinfection. This article looks at those findings from a practical water treatment perspective, with particular attention to swimming pool disinfection.
What Can 9,230 Water Samples Tell Us?
From 2016 to 2020, Vukić Lušić et al. tested 9,230 water samples in Primorje-Gorski Kotar County, Croatia. The study included 4,171 drinking water samples and 5,059 swimming pool water samples, making it possible to look at Pseudomonas aeruginosa across two different types of treated water.
P. aeruginosa was detected in 3.9% of drinking water samples and 4.6% of swimming pool water samples. In swimming pools, the researchers also observed a seasonal pattern, with detection occurring more frequently during the warmer period of the year.
The study did not stop at the overall positive rate. The 5,059 swimming pool samples came from different types of facilities and were evaluated alongside factors including pool characteristics, water temperature, season, and disinfection practices. When these results are separated by pool type, the differences become much easier to see.
Where Did Pseudomonas aeruginosa Occur More Often in Swimming Pools?
The overall 4.6% detection rate for swimming pool water does not tell the whole story. Once the samples were separated by pool type, the differences became much more noticeable.
The highest proportion of positive samples was found in entertainment pools, at 13.8%, followed by spa/hydromassage pools at 4.7%, children's and recreational pools at 3.9%, rehabilitation pools at 2.1%, and sports pools at 1.2%.
Why might some pools show higher occurrence than others?
Pool use is one possible factor. Entertainment facilities may have more complex structures and heavier or more varied usage, while spa and hydromassage pools often operate at higher temperatures. The study notes that entertainment pools can be more difficult to maintain because of their structural complexity and the potential for biofilm formation. For spa and hydromassage pools, higher temperatures, increased user sweating and skin shedding, and a smaller water volume per user can increase the amount of nutrients available to microorganisms.
There is also an interesting distinction between frequency of detection and concentration. Although rehabilitation pools had a lower positive rate of 2.1%, they showed the highest median P. aeruginosa concentration among the pool categories, at 20 CFU/100 mL. This is a useful reminder that simply counting positive samples does not always describe the whole water quality picture.
The study also found P. aeruginosa more frequently in freshwater pools (5.6%) than seawater pools (2.7%), while outdoor pools had a slightly higher positive rate than indoor pools, 4.9% versus 4.5%. Interestingly, the concentration of P. aeruginosa was higher in indoor pools despite their slightly lower positive rate.
Taken together, these findings suggest that there is no single pool environment that can be evaluated by one factor alone. Water temperature, pool design, user load, circulation, maintenance, and disinfection all form part of the picture.
Why Can Pseudomonas Persist in Water Systems?
P. aeruginosa is well adapted to aquatic environments and can colonize moist surfaces and materials that come into contact with water. One of the challenges is its ability to form biofilms. In water supply systems, biofilms can develop on pipe surfaces and other components, while in swimming pool systems, plumbing, filters, and other continuously wet areas can provide potential sites for microbial attachment.
Once microorganisms become established in a biofilm, simply treating the bulk water may not always address every potential reservoir in the system. Biofilm development can be influenced by factors including nutrient availability, water flow, temperature, pH, pipe materials, and the presence of disinfectants.
Swimming pools also have a constantly changing contamination load. Bathers can introduce microorganisms and organic substances into the water, while warmer water and intensive use can further increase the demands placed on the treatment system.
This helps explain why maintaining water quality is an ongoing process. The goal is not simply to add disinfectant when a problem appears, but to keep the entire treatment system operating under appropriate conditions.
What Does This Mean for Pool Disinfection?
The study provides an interesting perspective on the role of disinfection. Among the swimming pool samples, the researchers observed different P. aeruginosa detection rates depending on the reported disinfectant used.
The positive rates were:
- Hydrogen peroxide: 32.4%
- Sodium hypochlorite & Chlorine: 3.8%-4.8%
The lower detection rates observed in pools using chlorine-based treatment are relevant because they show why maintaining an effective disinfectant system remains an important part of pool water management. The study also found a negative correlation between P. aeruginosa and free residual chlorine, with 72% of samples in which P. aeruginosa was detected having a residual chlorine concentration below 0.5 mg/L. Based on these findings, the study indicates that chlorine should be maintained at a level sufficient to inactivate P. aeruginosa, with free residual chlorine approaching the lower end of the permitted range (ANSI/APSP/ICC-11 2019)—around 1 mg/L for standard swimming pools (indoor) and 3 mg/L for hot tubs (with cyanuric acid). Oxygen-based disinfectants are unreliable, as oxygen is not a dependable stabilizer and the available oxygen content of oxygen-based disinfectants depletes rapidly.
Where Do SDIC and TCCA Fit into Swimming Pool Water Treatment?
This is where the study's findings connect naturally with the products used in day-to-day pool treatment. Both sodium dichloroisocyanurate (SDIC) and trichloroisocyanuric acid (TCCA) are stabilized chlorine products that provide available chlorine for water disinfection. They can therefore be incorporated into swimming pool treatment programs where chlorine-based sanitation is required.
SDIC is available in forms as granules. Its relatively fast dissolution characteristics can be useful when flexible dosing or more rapid chlorine addition is needed. This makes it suitable for a range of routine pool water treatment applications.
TCCA, with its high available chlorine content, is commonly supplied in tablet or granular forms. TCCA tablets dissolve more slowly than SDIC products, making them useful in applications where feeder dosing is preferred.
The choice between SDIC and TCCA does not need to be viewed as a question of which product is universally better. In practice, factors such as the dosing method, pool size, treatment schedule, desired dissolution rate, and operating conditions all influence which product is more convenient for a particular system.
The important point is that both products can serve as chlorine sources within a broader pool sanitation program. Their role is to help maintain the required level of disinfection as water continues to circulate and new contaminants enter the pool.
What Can Pool Water Management Learn from the Study?
Perhaps the most useful lesson from the research is that microbial control is a continuous process. A pool can be visually clear and still require careful attention to its microbiological condition. Regular testing of disinfectant levels and other water quality parameters helps operators understand what is happening in the system rather than relying on appearance alone.
The study also shows why different facilities may need different levels of attention. High-use entertainment pools, warm spa facilities, and systems with complex structures may place different demands on water treatment. Where microbial problems persist, it can be useful to look beyond the water itself and consider filters, plumbing, circulation, surfaces, and possible biofilm reservoirs.
For chlorine-based treatment, maintaining an appropriate residual is particularly important. The study's findings support the practical value of monitoring free residual chlorine rather than assuming that adding a chlorine product automatically means the water is adequately disinfected.
For pool operators, the overall approach is therefore straightforward: choose a suitable disinfectant, apply it according to the system's requirements, monitor water quality regularly, and keep circulation, filtration, and physical maintenance working alongside chemical treatment.
Conclusion
The five-year Croatian study provides a useful look at Pseudomonas aeruginosa across two very different water environments. By examining more than 9,000 drinking water and swimming pool samples, it shows that occurrence can vary with the characteristics and operating conditions of each water system.
For swimming pools, factors such as pool type, temperature, user load, biofilm, and disinfectant management can all influence microbial control. Chlorine-based treatment remains an important part of this process, and products such as SDIC and TCCA provide practical sources of available chlorine for pool sanitation. Ultimately, good results depend not on one treatment step alone, but on choosing suitable products and maintaining the water treatment system consistently.
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Liuhe Chemicals is a professional manufacturer and supplier of SDIC, TCCA, Cyanuric Acid, Sulfamic Acid, and Melamine Cyanurate. Our products are used in water treatment, disinfection, and various industrial and specialty chemical applications. With a focus on consistent quality, reliable supply, and professional service, Liuhe supports customers worldwide with practical chemical products for different application requirements.
FAQ
What is Pseudomonas aeruginosa?
Pseudomonas aeruginosa is a microorganism commonly found in aquatic environments and other moist locations. It can survive and multiply under a range of environmental conditions and can form biofilms on suitable surfaces.
An opportunistic pathogen, it primarily infects immunocompromised people but can also infect healthy individuals. It causes hospital‑acquired infections including ventilator‑associated pneumonia, burn‑wound infections and otitis externa, and readily colonizes medical devices. Poorly maintained hot tubs and swimming pools may trigger hot‑tub rash and swimmer’s ear. Patients with cystic fibrosis or diabetes face higher infection risks. Species‑specific core genes contribute to its pathogenicity.
Which types of swimming pools had higher Pseudomonas detection rates?
Entertainment pools had the highest positive rate in the study, at 13.8%, followed by spa/hydromassage pools at 4.7%. Sports pools had the lowest rate among the categories studied, at 1.2%.
Can chlorine help control Pseudomonas aeruginosa in swimming pools?
Chlorine-based disinfection can play an important role in controlling microorganisms in pool water. The study observed a negative correlation between P. aeruginosa occurrence and free residual chlorine, supporting the importance of maintaining an appropriate chlorine residual.
What is the difference between SDIC and TCCA for swimming pools?
Both SDIC and TCCA are stabilized chlorine disinfectants that provide available chlorine. SDIC for pools is available in granular forms and can offer more flexible dosing and relatively faster dissolution, while TCCA is commonly used in tablet form where slower dissolution and feeder dosing are desirable. The appropriate choice depends on the pool's treatment system and operating requirements.
Is adding chlorine enough to control Pseudomonas in pool water?
Not by itself. Free chlorine in swimming pools is not a fixed value; it declines due to organic-matter consumption and sunlight-driven degradation, and may even drop abruptly, for example when pool load surges. If residual chlorine is poorly controlled and frequently falls below the minimum required level, bacteria can still grow during these gaps and trigger health issues. They may also attach to piping or suspended particles, creating persistent health hazards. Chlorine treatment works best as part of a broader water management program that also includes regular testing, appropriate pH control, circulation, filtration, equipment maintenance, and cleaning of pool surfaces and other potential microbial reservoirs.