Experiences with bacteriological monitoring of pool water

A bacteriological study was completed on pools and whirlpools operated by hotels and private health clubs in the metropolitan area of Toronto, Ontario, Canada. Coliform bacteria, fecal coliform bacteria, and fecal streptococci were found only when other indices showed a drastic deterioration in water quality. Aerobic plate counts were higher, and staphylococci and Pseudomonas aeruginosa occurred more often in whirlpools than in swimming pools. There was a correlation between aerobic plate counts and the presence of staphylococci and P. aeruginosa. P. aeruginosa was rare in swimming pools in the absence of staphylococci; however, in whirlpools the organism was often found in the absence of staphylococci, and when aerobic plate counts were low. P. aeruginosa and plate counts in excess of 3,000 per ml occurred more frequently in whirlpools when the free chlorine residual was less than one part per million. The surface film showed concentrations of staphylococci far greater than the pool water. Whirlpools appear to present a different ecosystem that favors the establishment of P. aeruginosa. Staphylococci, but not Staphylococcus aureus, are useful in indicators of pool water quality but better laboratory methodology is required. Additional attention should be directed to the bacteriology of the water surface film, which presents a more direct hazard to bathers.