CONTROL OF COLIFORM GROWTH IN DRINKING-WATER DISTRIBUTION-SYSTEMS

The occurrence of coliforms in drinking water distribution systems may be explained by (i) inadequate water treatment, (ii) post-treatment c ontamination, or (iii) coliform growth in the network. In order to con firm the third hypothesis, a 24 h-starved dense suspension of Escheric hia coli was injected into an experimental water distribution system. Results from this experiment clearly indicate that E. coli may find ec ological conditions in drinking water distribution systems which will allow growth, particularly in the biofilm phase. Chlorination is an ap propriate tool to limit coliform much more easily than the total heter otrophic bacterial biomass. However, in all cases, biofilm associated bacteria are more difficult to kill than suspended bacteria, because o f chlorine consumption by the pipe material, and because of a diffusio n-limited reaction between chlorine and the biofilm.