Mohawk Valley Water Authority (MVWA) recognized that an early warning system must reliably identify contamination events in source water or distribution systems in time to allow an effective response to prevent exposure. MVWA has examined and implemented several on-line monitoring systems and incorporated rapid methods into the daily water quality monitoring routine. This paper is a continuation of a case study presented at the 2002 WQTC and the 2003 Water Security Congress examining the equipment and methods chosen by MVWA. The installation, modifications and implementation of the methods chosen are chronicled along with the problems encountered, an evaluation of the reliability of the data generated and the approach adopted by MVWA to interpret the data generated by the EWS. The case study evaluates rapid methods including flow cytometry and vital dyes for evaluation of Total Biomass and Total Viable Organisms (TVO) in water, real time PCR for identification of pathogenic microorganisms, and the evaluation of several toxicity testing methods utilizing luminescent bacteria, Daphnia magna and submitochondrial particles. After a successful pilot installation, on-line microchips used to monitor water quality parameters were installed by MVWA at several strategic locations in the distribution system. This study examines the installation of the microchips and the telemetry devices, the problems encountered, the design of an autosampler programmed to take water samples when a preset water quality parameter has been violated and the integration of the data generated by the microchips into the SCADA system. The study also evaluates the installation and use of an online gas chromatograph (GC) used to monitor source waters for volatile organic chemicals. In addition, MVWA has developed a water quality model and considers it to be a critical component of our early warning system. Equally important is the preparation of a process or plan that provides guidelines for the type and extent of a response to an alarm. The EWS has many pieces that must be carefully chosen and put into place to complete the puzzle unique to each water system. Includes 24 references, tables, figures.