HOW AND WHY HAZARDOUS EVENTS ARE MONITORED IN YOUR WATER

Early or advance warning systems are used to detect any sudden deterioration in the quality of the source drinking water supply either just before the water goes into the distribution system or some distance upstream. They are meant to supplement conventional monitoring by quickly providing timely information on unusual threats to a water supply. Early warning systems are much more common for riverine source waters than impoundments or ground water supplies, and are most typically established in response to chemical and radioactive threats rather than pathogens.

The need for and scope of an early warning monitoring system should be guided by an assessment and prioritization of site-specific risks that includes a vulnerability analysis of the entire water supply system, including the watershed and distribution system. Threats should be prioritized based on their probability of occurrence and the severity of their impact.

Of the many potential catastrophic threats to water supplies, including natural, recurring events and anthropogenic- related events, managers of drinking water utilities perceive the most significant threats to be:

1. spills of oil and industrial products from tanks, pipelines, or transportation,
2. insecticides and herbicides from agricultural runoff, and
3. pathogens from untreated sewage discharges.

The number of intentional threats and acts of sabotage against water supply systems is relatively small, and hoaxes are much more likely. Intentional threats include: (1) destruction of parts of a system, either by physical destruction or computer hacking, and (2) contamination of the system with chemicals, microbes, toxins, or radioactive compounds. The main lines of defense against physical and cyber acts of destruction and contamination include the design of a redundant water treatment and distribution system and denial of access. Maintenance of adequate chlorine residual in the distribution system and increasing it in times of perceived or real danger provide additional protection from microbial threats. However, many pathogens are resistant to chlorine, and the effectiveness of disinfectants on some biowarfare microbes is not known. Also, the use of chlorine must be balanced with concerns over the formation of by-products.

Research needs for threat assessment include a quantitative assessment of threats and susceptibility of various types and sizes of water supplies, a study of the redundancy of water distribution systems to determine their vulnerability to physical destruction, and an analysis of the costs and procedures required to upgrade the security of water supplies.

What is the goal of early warning monitoring systems? The goal of an early warning monitoring system is to reliably identify low probability/high impact contamination events (chemical, microbial, radioactive) in source water or distribution systems in time to allow an effective local response that reduces or avoids entirely the adverse impacts that may result from the event.

Requirements for the ideal early warning system:

• Provides warning in sufficient time for action
• Is affordable
• Requires low skill and training
• Covers all potential threats
• Is able to identify the source
• Is sensitive to quality changes at regulatory levels
• Gives minimal false positive or negative responses
• Is robust Is reproducible and verifiable
• Allows remote operation
• Functions year-round

Because of the costs involved in the implementation of early warning monitoring systems, several factors must converge to support their implementation. Costs versus benefits will be determined at the local level, and support will generally increase as the risk or perception of risk of serious illness increases.

Risk or the perception of risk will increase as the presence or effectiveness of existing barriers (e.g., chlorination for pathogens) decreases, as the seriousness (perceived or real) of the potential illness increases, and as the size of the affected population increases, among other factors. Because no monitoring system can be constructed to detect all threats, monitoring of health effects in the community using enhanced surveillance strategies to provide early detection of epidemics should be considered an additional line of defense.

Microbial research needs include more timely procedures for analysis, methods to detect biowarfare agents and newly emerging pathogens, development of expert systems for responding to unusual events and better indicators of water quality that can instantaneously detect and quantify hazards in the water distribution system, and research to determine the effectiveness of chlorine or other disinfectants for controlling biological warfare agents.