AWWA C670-25 Online Chlorine Analyzer Operation and Maintenance (PDF)

Continuous chlorine residual monitoring is used for two primary purposes: process control and regulatory compliance. Process control implies that the reason for testing the chlorine content of water is primarily to determine how well a process is working (e.g., how consistent the chlorine residual is downstream of the mixer or contact tank, how much chlorine is consumed after disinfection, etc.), to control chlorine feed equipment, and to ensure appropriate chlorination of the final product. The efficiency of monochloramine formation may be controlled by the total chlorine residual (for regulatory reporting purposes) and free ammonia concentration to maintain an acceptable chloramine speciation. Process control may also imply analyzing residual chlorine content in distribution or transmission systems. A sudden decrease in measured chlorine residual may be indicative of malfunctioning equipment, system failure, untreated water intrusion, or introduction of some chlorine-consuming contaminants.
Testing the chlorine content of water primarily for regulatory compliance often involves testing method constraints, including sample collection point, analysis methods, sample interval, and chlorine residual targets. If testing is for regulatory compliance, the authority having jurisdiction (AHJ) shall be consulted prior to purchasing an online chlorine analyzer.
The purpose of this standard is to provide the minimum requirements for online chlorine analyzer O&M, sampling requirements, accuracy and precision testing requirements, range requirements, and methods of calibration and troubleshooting.