本文讨论了饮用水中微生物风险评估、与此类分析相关的问题、特定生物体的方法、证明达到风险水平所需的监测，以及如何进行风险评估，以确定是否避免贾第虫和病毒的给定风险水平。建议制定指导方针，确定必要的处理水平，以确保消费者获得成品饮用水，每年每10000人中有不到一人感染贾第虫和肠道病毒的风险。 包括52个参考文献、表格和图表。

This article discusses the assessment of risk from microorganisms in drinking water, the problems associated with such an analysis, the approach for specific organisms, the monitoring required to demonstrate that risk levels are met, and how risk assessment might be approached for determining whether a given level of risk from Giardia and viruses is avoided. Guidelines are suggested for determining the level of treatment necessary to ensure that consumers receive a finished drinking water with risks of less than one infection per 10,000 people per year from Giardia and enteric viruses. Includes 52 references, tables, figures.