The biological stability of treated drinking water has become a major concern for water utilities. The U.S. E.P.A. is concerned from the perspective of coliform MCL compliance and remediation of coliform biofilm problems. The levels of readily assimilable nutrients present in treated water are affected by water treatment processes, but of greatest concern are those processes, such as ozonation, that cause increases in the levels of assimilable organic carbon (AOC) and therefore contribute to biological instability of the water. Thus, the combined use of ozonation (pre-oxidant) and a lower disinfectant residual as an approach to reducing disinfectant byproducts may result in increased bacterial growth, including coliforms, in the distribution system. Information is needed on: the AOC flux level that stimulate coliform growth in biofilm: the specific nutrients and concentrations that can stimulate growth of both coliforms and HPC; treatment strategies to reduce AOC levels and strategies to effectively control biofilm formation where AOC levels cannot be reduced.

"EPA600/D-89/267"