1 The Research Institute of The Hospital for Sick Children, Toronto, Canada
Adequate inactivation of potentially pathogenic human viruses and bacteria in swimming pool waters has been attained by maintenance of free residual chlorine levels of 0.2 to 0.5 ppm at pH between 7 and 8. Similar residuals of free bromine or free iodine have inactivated six common enteroviruses and parainfluenza-1, and although they have inactivated enteric bacteria satisfactory in swimming pools, further tests are required to determine their viricidal efficiency. The virtual absence of enteric bacteria from swimming pools or wading pools with detectable free chlorine residuals contrasts sharply with the relatively frequent occurrence of high bacterial counts in unchlorinated lake waters or wading pools. However, chemical evidence of pollution, on the basis of concentrations of ammonia nitrogen, organic nitrogen, and chloride, was greatest in recirculating swimming pools, less in overflow-refill swimming pools, and least in freshwater lakes.
Submitted on October 26, 1962