Soft deposits, the key site for microbial growth in drinking water distribution networks

In this project we studied the microbiological quality of soft pipeline dep osits removed from drinking water distribution networks during mechanical c leaning. Drinking water and deposit samples were collected from 16 drinking water distribution networks located at eight towns in different parts of F inland. Soft pipeline deposits were found to be the key site for microbial growth in the distribution networks. The microbial numbers in the soft depo sits were significantly higher than numbers in running water. The highest m icrobial numbers were detected in the main deposit pushed ahead by the firs t swab. The deposits contained high numbers of heterotrophic bacteria, acti nomycetes and fungi. Also coliform bacteria were often isolated from deposi t samples. Manganese and copper in the deposits correlated negatively with the numbers of heterotrophic bacteria. After a year, the viable microbial n umbers in the new deposits were almost as high as in the old deposits befor e the first mechanical cleaning. The bacterial biomass production was highe r in the new than in the old deposits. (C) 2001 Elsevier Science Ltd. All r ights reserved.