Biological Stability of Drinking Water in Selected Water Distribution Systems

Results of microbiological analysis and biological stability of surface and groundwater (taken, treated and distributed in the Tri-city region) which supply a distribution system with low contact surface to transferred water volume ratio (approximate to 0.65) were presented. Additionally, the effectiveness of technological processes in reduction of the total number of bacteria (TNB) was evaluated and laboratory tests determined the susceptibility of water introduced into the system to the bacterial regrowth. It was established that high elimination (95%) of TNB occurred in the conventional surface water treatment system, while simple groundwater treatment systems were not effective in eliminating these bacteria. TNB was demonstrated to increase (even up to 20%) as a result of periodic leaching of bacteria from filters. In both surface and groundwater supply systems an increase in the TNB was observed. It was higher along the surface water network (330% for a 6-km section) than the non-disinfected groundwater network (170% for a 8-km section). The laboratory studies confirmed the beneficial effect of treatment processes on reduction of water susceptibility to bacterial regrowth. Increase in the total number of bacteria in the treated groundwater after 7-day incubation at temperatures ranging from 5 to 10 degrees C was approximately 80% lower than in the raw water.