本文描述了水务人员为确定在其服务区域观察到的地方性贾第虫病水平是否可归因于地表水供应所做的努力，地表水经过氯胺化处理，但未经过滤。将公用事业公司所在县的流行病学数据与另一个使用常规处理水的县的数据进行比较，发现贾第虫病的发病率、风险类别和年龄分布相似。贾第虫病病例的位置与未过滤水分配系统内的消毒接触时间之间没有相关性。 包括18个参考文献、表格、图表。

This article describes the efforts of water utility personnel to determine whether the level of endemic giardiasis observed in their service area could be attributed to the surface water supply, which is chloraminated but not filtered. Comparison of epidemiological data for the county in which the utility is located with data from another county that used conventionally treated water showed similar incidence rates, partitioning into risk categories, and age distributions for giardiasis. There was no correlation between the location of a giardiasis case and disinfection contact time within the unfiltered water's distribution system. Includes 18 references, tables, figures.