Water quality monitoring sensor equipment may be used to monitor key elements of water or wastewater treatment processes (such as influent water quality, treatment processes, or effluent water quality) to identify anomalies that may indicate threats to the system. Some sensors, such as sensors for biological organisms or radiological contaminants, measure potential contamination directly, while others, particularly some chemical monitoring systems, measure "surrogate" parameters that may indicate problems in the system but do not identify sources of contamination directly. In addition, sensors can provide more accurate control of critical components in water and wastewater systems and may provide a means of early warning so that the potential effects of certain types of attacks can be mitigated. One advantage of using chemical and biological sensors to monitor for potential threats to water and wastewater systems is that many utilities already employ sensors to monitor potable water (raw or finished) or influent/effluent for Safe Drinking Water Act (SDWA) or Clean Water Act (CWA) water quality compliance or process control.

Chemical sensors that can be used to identify potential threats to water and wastewater systems include inorganic monitors (e.g. chlorine analyzer), organic monitors (e.g. total organic carbon analyzer) and toxicity meters. Radiological meters can be used to measure concentrations of several different radioactive species. Monitors that use biological species can be used as sentinels for the presence of contaminants of concern, such as toxics. At the present time, biological monitors are not in widespread use and very few bio-monitors are used by drinking water utilities in the U.S.

Monitoring can be conducted using either portable or fixed-location sensors. Fixed-location sensors are usually used as part of a continuous, on-line monitoring system. Continuous monitoring has the advantage of enabling immediate notification when there is an upset. However, the sampling points are fixed and only certain points in the system can be monitored. In addition, the number of monitoring locations needed to capture the physical, chemical, and biological complexity of a system can be prohibitive. The use of portable sensors can overcome this problem of monitoring many points in the system. Portable sensors can be used to analyze grab samples at any point in the system, but have the disadvantage that they provide measurements only at one point in time.

Because of the direct threats to drinking water systems, the chemical, biological, and radiological sensors described in the subsequent Product Guides have primarily been used for source water and water distribution applications. However, the same technology can also be used in wastewater security, primarily for detecting disruptions in the treatment process. This guide on chemical and biological sensors covers the following individual products:

Chemical Sensor - Arsenic Measurement System

Chemical Sensor - Chlorine Measurement System

Chemical Sensor - Total Organic Carbon Analyzer

Radiation Detection Equipment

Radiation Detection Equipment for Monitoring Water Assets

Toxicity Monitoring/Toxicity Meters

Chemical Sensor for Toxicity (Adapted BOD Analyzer)

Biological Sensors for Toxicity