HETEROTROPHIC MICROORGANISMS IN DISTRIBUTION SYSTEMS FOR DRINKING WATER
Raw water, treated water and distributed water from three water works in the vicinity of Oslo, Norway, were investigated for content of heterotrophic, aerobic microorganisms and total count of bacteria. The treatment was different in the three water works, but they all got raw water from the hypolimnion of stratified lakes. The total counts were found to be about 3 orders of magnitude higher than the maximum count of colonyforming units, CFU, which again was much higher than the 3- and 7-days normal plate count at 20°C. Because of all the experience gained with the 3-days CFU, this analysis is recommended as the main parameter for presence of heterotrophic bacteria in distributed drinking water. The 7-days CFU’s may be used to check the efficiency of the disinfection process, especially when the process does not leave a residual disinfectant in the water. It is also a useful parameter for aftergrowth in the distribution network. “Complete abstract not presented.”