此前，人们认为不含大肠菌群的自来水不太可能引起水传播疾病。然而，在没有违反1975年或1989年总大肠菌群最高污染物水平（MCL）的供水系统中，已经报告了疾病暴发（尤其是贾第虫或隐孢子虫引起的暴发）和地方性水传播疾病风险。以1975年的规则为重点，利用大肠菌群数据和关于疫情的调查报告，作者比较了有和没有经历疫情的供水系统的MCL违规情况。在疫情调查期间，通常在公共系统中发现大肠菌群，但在疫情爆发前的几个月，只有一半的系统中检测到大肠菌群，只有四分之一的系统违反了MCL。发生疫情的社区系统与未发生疫情的社区系统之间的违规率没有显著差异； 通常两人都会遇到MCL。为了保护公众免受水传播疾病的影响，微生物监测必须辅以定期的卫生调查和活动，以确保适当的水质。包括14个参考文献和表格。

Coliform-free tap water has previously been thought to be unlikely to cause waterborne disease. However, disease outbreaks (especially those caused by Giardia or Cryptosporidium) and endemic waterborne disease risks have been reported in water systems that have not violated either the 1975 or 1989 maximum contaminant level (MCL) for total coliforms. Focusing on the 1975 rule and using coliform data and investigative reports about outbreaks, the authors compared MCL violations for water systems that did and did not experience an outbreak. Coliforms were usually found in a public system during an outbreak investigation, but in the months before an outbreak, they were detected in only half of the systems and caused an MCL violation in only one fourth of them. The violation rate was not significantly different between community systems that experienced an outbreak and those that did not; usually both met the MCL. To safeguard the public against waterborne disease, microbiological monitoring must be supplemented with periodic sanitary surveys and activities that ensure adequate water quality. Includes 14 references, tables.