在处理厂停止使用余氯之前和之后，对分配系统中饮用水的微生物数据进行了比较。对氯化地下水的细菌学评估一致显示异养平板计数（HPC）和lt5菌落形成单位（cfu）/mL，这表明细菌再生的可能性非常小。由于产生约0.1 mg/L游离余氯的氯化反应会导致味觉和气味投诉，因此停止了氯化反应，并分配了不含余氯的水。在这一变化后不久，保留时间较长的样品产生的HPC高达60- 80 cfu/mL。四到六周后，这些计数再次下降到lt5 cfu/mL。HPC的这种短期增加（在其他情况下也观察到）被认为是由于生物膜的变化。包括7个参考文献、表格、图表。

Microbiological data on drinking water in a distribution system were compared before and after the treatment plant discontinued use of a chlorine residual. Bacteriological assessments of chlorinated groundwater consistently showed heterotrophic plate counts (HPCs) <5 colony forming units (cfu)/mL, a count indicating that bacterial regrowth was very unlikely. Because chlorination that produced about 0.1 mg/L free chlorine residual led to taste and odor complaints, chlorination was discontinued, and water that contained no residual was distributed. Shortly after this change, samples with higher retention times produced HPCs as high as 60-80 cfu/mL. After four to six weeks these counts decreased to values again <5 cfu/mL. This short-term increase in HPCs, which has also been observed in other cases, is assumed to be due to a change in the biofilm. Includes 7 references, table, figures.