A biofilm based method was used to measure the biological regrowth potential of water by a biofilm annular reactor. The tested water was taken from the city distribution system at the lower reaches of Yellow River. Bacterial growth data, including biofilm and suspended bacteria in water, were collected during the month-long study and compared with turbidity and the traditional biodegradable organic material measuring method, namely, assimilable organic carbon (AOC) method. The change trends of biofilm biomass, heterotrophic plate counting of suspended bacteria (HPCs), turbidity and AOC were discussed and the correlation between these indicators were analyzed in this study. Results of this study indicated that comprehensively quantitative biostability factors should take into account both biodegradable organic material and biofilm formation capability of tested water.