In the context of water quality reporting, COC stands for:

• A. Contaminant of Compliance
• B. Contaminant of Concern
• C. Contaminant of Calibration
• D. Concentration of Contaminants

Answer: (B)

In water quality reporting, a COC is the Contaminant of Concern—the specific contaminant that is being tracked because of its health risk or regulatory significance for the system. This label helps utilities focus reporting and surveillance on substances that require attention, such as those with action thresholds, potential exceedances, or ongoing monitoring requirements. By tagging results with the Contaminant of Concern, data systems and public reports can clearly indicate which substances need scrutiny and possible remedial steps. The other options don’t fit because a contaminant of calibration refers to instrument calibration, not a contaminant being monitored; concentration of contaminants describes a measurement, not a designated contaminant; and contaminant of compliance isn’t a standard label used in reporting. In practice, substances like lead, arsenic, or nitrate may be designated as the Contaminant of Concern when they pose a risk or have monitoring requirements in a particular context.