This slide presentation outlines information on a web-based Early Warning System (EWS) for water suppliers along the Schuylkill and Delaware Rivers in Pennsylvania and New Jersey, including the Phildelphia Water Department. The EWS facilitates communication among first responders and water suppliers during acute water quality events. This intranet portal to shared real-time, near real-time, and historic water quality data, is optimized for geospatial visualization of water supply risks and hazards flowing within the rivers. Key technical features of the system include: integrated GIS and time of spill travel model geocode event locations and predict times of arrivals of hazards at affected intakes; common intranet portal to shared real-time, near real-time, and historic water quality data; telephony and email based notification subsystems; XML and DHTML architecture assures data quality, operator effectiveness, cost effective and rapid system improvement and evolution; and, data model support of spatio-temporal water quality analyses. Includes figures.