Free residual chlorine is a disinfectant added during water treatment to kill harmful microbes. A small amount remains in tap water to ensure continued protection.

Free residual chlorine is added to drinking water as the final step in treatment. It effectively kills harmful bacteria and viruses, with a small amount remaining to protect water quality as it travels through distribution systems. Typically measured in parts per million (ppm), chlorine levels are carefully monitored to balance safety and taste. This practice has been crucial in preventing waterborne diseases for over a century, making it a cornerstone of public health efforts worldwide.