On-line water quality parameters : as indicators of distribution system contamination

The safety and security of drinking water distribution systems have recently generated considerable interest because of the credible concern that they could be compromised with chemical, biological, and radiological contaminants. In order to protect public health, the US Environmental Protection Agency initiated a program to investigate how changes in water quality parameters, which potentially indicate contamination, can be detected by real- or near real-time sensors. The sensors investigated were off-the-shelf commercial products designed to monitor standard drinking water parameters such as pH, free chlorine, oxidation reduction potential (ORP), dissolved oxygen, specific conductance, turbidity, total organic carbon (TOC), chloride, ammonia, and nitrate. These sensors were mounted within a recirculating pipe loop and challenged with contaminants including secondary effluent from a wastewater treatment plant, potassium ferricyanide, a malathion insecticidal formulation, a glyphosate herbicidal formulation, nicotine, arsenic trioxide, aldicarb, and Escherichia coli K-12 strain with growth media. Overall, the sensors that responded to most contaminants were those that monitored for free chlorine, TOC, ORP, specific conductance, and chloride. Generally, the technology used in sensor design or the particular manufacturer of the sensor did not affect the response characteristics. These results may help refine the role of water quality sensors, in conjunction with other data sources such as customer complaints and public health surveillance data, in a contamination warning system within a water distribution system.