Introduction: The process of preparing pool water is called disinfection. One of them is the chemical disinfection of bathing water with the electrolysis of sodium chloride (NaCl). The efficiency of the disinfectant is expressed as Ct, where "C" is the concentration of the disinfectant (mg/L), and "t" is the contact time for the inactivation of a certain percentage of microorganisms. Instead of a percentage, the log10 value is used, which is called logarithmic inactivation, written as N0/Nt = e^(k*t). Objective: The purpose of this master's thesis is to investigate whether the NaCl electrolysis process causes the formation of chlorine in bathing water and thus enables the proper maintenance of the hygienic condition of the bathing water over an extended period. We also aim to demonstrate the effectiveness of disinfection by a reduction of test bacteria E. coli and E. faecalis by three logarithmic stages in a privately owned pool with a volume of 32 m3.Methods: We used test bacterial cultures E. coli and E. faecalis to contaminate the pool water. The suspension of test bacteria E. coli and E. faecalis for pool contamination was prepared in the laboratory of the Veterinary Unit of the Slovenian Armed Forces (SV). We took 6 samples (V0 to V6). V0 represented the water sample before the experiment, V1 before pool contamination, V2 one hour after contamination, and V3, V4, and V5 after turning on the electrolysis. Bacterial counts were determined in the laboratory of the Veterinary Unit SV. Results: Sample V0 complies with the regulations and represents the maintenance of the hygienic condition of the pool water. The disinfection process is effective since the number of bacteria E. coli and E. faecalis decreased by three logarithmic stages in 44 minutes at 0.15 mg/L of free chlorine. Discussion and Conclusion: Electrolysis with NaCl ensures the formation of free chlorine. We have confirmed that the concentration of free chlorine in the pool water complies with the regulations and allows disinfection with a residual effect, with pH value correction and strict adherence to manufacturer's instructions. Using the electrolysis NaCl disinfection process, the number of bacteria E. coli and E. faecalis decreased by three logarithmic stages, and the bathing water complies with the regulations on minimal hygiene requirements for swimming pools and bathing water (Official Gazette of the Republic of Slovenia, No. 59/15, 86/15-corr., and 52/18).
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