An effective contamination warning system (CWS) should be able to identify deviations from established baselines and system anomalies in a timely manner by integrating and analyzing information from online water quality monitoring, sampling and analysis, enhanced security monitoring, consumer complaints, and public health surveillance. The WaterSentinel (WS) approach for a CWS involves the active deployment and use of monitoring technologies/strategies that are not contaminant-specific and enhanced surveillance activities to collect, integrate, analyze, and communicate information from a variety of sources. These information streams are utilized to provide a timely warning of potential water contamination incidents and initiate response actions to minimize public health and economic impacts. As part of an effective CWS, a method for event detection should be developed such that it can quickly recognize true contamination incidents while minimizing the occurrence of false positives. An effective event detection system, coupled with the other components of the WS-CWS, should contribute to the CWS goal of reliable and timely detection of contamination to protect public health and water system infrastructure.