How do residual chlorine levels in tap water compare to swimming pools and why does pool water smell so strongly?

How do residual chlorine levels in tap water compare to swimming pools and why does pool water smell so strongly?
China's drinking water standard (GB 5749-2022) allows free chlorine up to 2 mg/L at the plant and 0.05-2 mg/L at the tap—twice the 0.3-1.0 mg/L range for swimming pools (GB 37488-2019). The reason is exposure: pool water contacts eyes and mucous membranes for extended periods, while drinking water passes through the stomach's higher tolerance. The strong 'chlorine smell' at pools is actually not free chlorine (HOCl/OCl⁻), which is nearly odorless. It comes from chloramines—especially trichloramine (NCl₃)—formed when urea and sweat react with residual chlorine. These disinfection by-products (DBPs) irritate eyes and reduce water surface tension, creating that slippery film on skin. The real health concern is DBP formation, not residual chlorine itself.