Research objectives: Monitor the composition of biofilms in a closed pool model in situ during the application of different disinfection methods. To determine the effectiveness of disinfection methods, UV radiation and chlorination, on the ability to form biofilm as well as on the destruction of mature bacterial biofilm created on ceramic tiles in vitro. Characterize pool water in an in situ model by measuring physical, chemical and microbiological indicators and the influence of sanitation methods on selected indicators. Methods: Examination of biofilm composition in in situ conditions was carried out on additionally placed ceramic tiles in a closed pool model, with different disinfection methods. The total number and share of individual species in the mixed biofilm was quantified. The sensitivity of isolated bacterial species to antibiotics was tested. The physical, chemical and microbiological indicators of the pool water were monitored comparatively using accredited methods. The in vitro part of the research was conducted on the bacterial species Pseudomonas aeruginosa, Pseudomonas fluorescens, Pseudomonas stutzeri and Burkholderia cepacia. The effect of sodium hypochlorite and UV radiation on the ability to form biofilm and on mature biofilm was examined. Biofilms were quantified by determining CFU/ml. A qualitative analysis of the biofilm was performed using scanning electron microscopy. Results: The combination of UV radiation and chlorination is the most effective in inhibiting biofilm formation as well as in reducing mature biofilm. The amount of mixed biofilm created in the in situ model was reduced during the application of the combined disinfection method. The combined disinfection method reduced the content of harmful byproducts and ensured optimal values of the physical, chemical and microbiological indicators of the pool water. Conclusion: UV radiation and chlorination as disinfection methods are not effective enough in suppressing biofilm formation. The combined action of these methods can enhance the antibiofilm effect. With regularly implemented sanitation methods in the pool model, using a combined disinfection method, the biofilm in the pool can be controlled, but not completely removed. Our results Results of this research can contribute to the development of new disinfection methods that, in addition to water disinfection, will also affect the pool's biofilm. Combined pool water disinfection methods reduce the amount of harmful byproducts of chlorine disinfection.