CONTAMINATION WARNING SYSTEM
A Contamination Warning System (CWS) is an integrated
system (sensors and software) aimed at detecting water
quality deviations. An event detection system detects water
quality events and scales them according to their threat level.
This can be as simple as recording the magnitude of the change
detected or as advanced as recognising certain properties in the
event response, and classifying the event. Most event detection systems are designed to detect anomalies (e.g. changes not due to water quality variations over the course of normal operations), while attempts at actual event classification have been less successful.
A CWS provides automated response to water quality anomalies based on information from a number of disparate data streams (e.g. OWQM, LIMS, CIS, Security, PHS). These systems are online 24/7 and respond in real-time. They can detect changes in water quality that are too small to be visible to an operator, especially if the systems use pattern recognition to analyse signals coming from multiple sensors or multiple sensor locations. Early detection of water quality events allows timely responses, for example, allowing isolation of the contaminated water and reduction of consumer exposure to the contaminated water through rapid response to alerts.
A CWS needs to be calibrated with event free sensor data collected under real-life conditions. This data represents normal dynamics in water quality and is used to adjust the sensitivity of the event detection algorithms and to train the system on normal conditions. If this is not properly done, the system will respond to normal changes, generating false positive alarms. Calibration of the system consists of maximising sensitivity while keeping the number of false positive alarms to a minimum acceptable level. A high false alarm rate will lead to lack of trust in the capabilities of the CWS and real events will be ignored.
Consequence Management Plan
Developing, practicing, and training on response protocols is a critical component of a Contamination Warning System. The US EPA Water Security Division worked with major utilities across the United States to develop a standard approach to evaluating and responding to unusual water quality events. The approach is a tiered structure that escalates the degree of response based on the level of information available to a utility. This methodology addresses internal and external notification procedures, data collection processes, and public outreach notifications. Regardless of the type and sophistication of the CWS that utilities implement, a Consequence Management Plan is considered to be one of the first areas to focus on.