This article suggests a more objective approach to evaluating the condition of a water system - including source, treatment, and distribution - based on performance data. Most groundwater systems are currently evaluated by managers and regulators through a combination of compliance monitoring and sanitary survey inspections. However, field experience has demonstrated types of monitoring that can be performed at groundwater systems to comprehensively evaluate their ability to resist microbiological contamination. Utility managers will benefit from this information because it shows how process-control-type monitoring, compared with nonregulatory goals, can help improve utilities' ability to prevent contamination. It is hoped that the information provided will encourage groundwater utilities to begin collecting and analyzing performance data and lead to a better understanding of how each barrier can be improved. Includes 12 references, tables, figure.