overchlorination

Overchlorination is the condition in which chlorine is added to a water system at concentrations higher than those needed for effective disinfection, resulting in elevated residual chlorine levels. It can occur in drinking water treatment, swimming pools, industrial cooling systems, and other water-handling contexts.

In drinking water, overchlorination can cause taste and odor problems and, over time, promote the formation of disinfection byproducts such as trihalomethanes and haloacetic acids, especially when organic matter is present. In swimming pools and spas, excessive chlorine can irritate the eyes, skin, and respiratory tract, and produce strong odors. High chlorine levels can also accelerate corrosion of metal components and degrade certain plastics or seals.

Causes of overchlorination include dosing errors, malfunctioning residual-control equipment, sudden changes in water flow or temperature, and the addition of chlorine when the system is already saturated with residuals. Environmental factors such as high organic content or sunlight exposure can influence the rate at which chlorine reacts, sometimes contributing to elevated perceived chlorine effects even if actual residuals are fluctuating.

Management and prevention focus on accurate residual monitoring, proper dosing, and system maintenance. Regular verification of chlorine and pH levels, automatic feed systems with feedback control, thorough flushing of lines, and, when needed, dechlorination or aeration are common approaches to mitigate overchlorination. Regulatory guidance and health-based thresholds vary by jurisdiction but generally emphasize maintaining residuals within advised ranges to ensure disinfection while minimizing taste, odor, and safety concerns.