这篇文章提出的证据表明，监测样本中大肠菌群的平均数量对分布系统的平均大肠菌群密度的估计很差。本文讨论了导致这一结论的各种研究结果。证据包括大肠菌群计数的差异、样本数量的不足、检测方法的局限性导致的数据截断、样本采集和检测期间储存期间样本密度的变化，以及可能由于样本在运送至实验室期间大肠菌群密度的变化而产生的虚假结果，采样水中的浊度或非大肠菌群，大肠菌群的生理状态，大肠菌群的种类，或采样和分析协议。建议根据大肠菌群密度大于预选限值的监测样本比例制定法规，作为当前微生物最大污染物水平的可行替代方案。 包括28个参考文献和表格。

This article presents evidence that the average number of coliforms in monitoring samples is a poor estimate of the mean coliform density of the distribution system. Results of various studies that led to this conclusion are discussed. The evidence includes variance in coliform counts, inadequacy of sample numbers, data truncation caused by limitations of the examination methods, changes in sample densities during storage between the time of sample collection and time of examination, and false results that may be due to changes in the coliform densities of samples during transit to the laboratory, turbidity or noncoliform bacteria in the water sampled, the physiological state of the coliforms, the species of coliforms, or sampling and analytical protocols. A regulation based on the fraction of monitoring samples with coliform densities greater than a preselected limit is recommended as a feasible alternative to the current microbiological maximum contaminant level. Includes 28 references, tables.