I refer to King Y. S. Ho's letter 'Dangers of chlorine as swimming pool disinfectant' (South China Morning Post, August 3).
According to the Director of Electrical and Mechanical Services, the disinfecting systems for public swimming pools have widely adopted ozone as the principal disinfectant, with chlorine providing the residual in the body of the pool to prevent cross-contamination between swimmers. This kind of disinfecting system is commonly used in other countries for public swimming pools.
The free residual chlorine concentration in the water should be maintained at not less than 0.5 parts per million (ppm) at all times during which the swimming pool is in use by bathers. Should chlorine be used as the sole disinfectant, a higher level of the minimum concentration, of 1ppm, is required.
It is the department's understanding that both chlorine and bromine can be used to supplement the ozone system. However, chlorine is more widely used because of its stability under ultraviolet exposure and the lower operating and maintenance costs of the associated system.
The Department of Health was also consulted and it advised that, so far, there is no evidence to support that users of chlorinated pools have a greater risk to their health than those using pools with other types of disinfectant.
Bromine-based disinfectants decompose upon sunlight and the bromine concentration is thus difficult to maintain. The microbiological quality of water is also less easily controlled by bromination than chlorination.
