Determinants of the microbiological water quality of indoor swimming-pools in relation to disinfection

A study of microbiological water quality at 12 indoor swimming-pools was carried out over a three-month period. Chlorination was used as the disinfectant method at seven of them and at the other five electrolytically generated copper and silver ions were used. A regression analysis was used to evaluate the association between variables linked to disinfection and physico-chemical water quality—residual free chlorine (HOCl+OCl−), Cu, Ag, pH, conductivity, turbidity—and microbiological water quality—aerobic plate count, total and fecal coliforms, fecal streptococci, Pseudomonas aeruginosa and Staphylococcus aureus. Analysis showed that the sole predictive variable was disinfectant concentration based on the linear model P=a+bX (P=probability that a sample be microbiologically acceptable; a=interception; b=gradient, and X=disinfection concentration). At the chlorinated pools 2.6 mg l−1 of free chlorine (a=0.34, b=0.21) was required, and at those using Cu–Ag 3.4 mg l−1 of Cu (a=0.15, b=0.22) in order to ensure that there be a 90% probability of the bathing water being microbiologically acceptable. The active chlorine concentration (HOCl) failed to present an association with microbiological water quality.