Comparison of shower filters for reducing total residual chlorine under household flow conditions

Tap water is disinfected to prevent microbial contamination, but chlorine-based disinfectants, such as chloramine, may contribute to skin irritation in individuals with sensitive skin conditions such as atopic dermatitis. We evaluated two commercial shower filters, specifically a low-cost 4-stage filter and a widely sold 20-stage filter, along with three filtration media commonly used for chlorine removal in commercial shower filters: calcium sulfite (CaSO₃), Kinetic Degradation Fluxion (KDF) 55, and granular activated carbon (GAC). We hypothesized that the two commercial filters would perform similarly to each other in their ability to remove chlorine, and that chlorine removal effectiveness would differ among the three individual media. We measured total residual chlorine concentrations before and after filtration under controlled low- and high-flow conditions using a colorimetric method. Under both flow conditions, the 4-stage and 20-stage filters significantly reduced total residual chlorine, with no statistically significant difference between them. When we tested each medium individually, CaSO₃ achieved chlorine reduction comparable to that of both commercial filters at both flow rates, while KDF 55 and GAC showed limited effectiveness, particularly under high-flow conditions where chlorine removal rates were only about 17%. These findings suggest that CaSO₃ plays a central role in chlorine removal during shower use and provide preliminary evidence supporting the design of low-cost and reusable shower filters.