Legal, and still worth filtering: the trihalomethane story
Chlorine keeps water free of bacteria — and reacts to form byproducts that the federal limit allows at hundreds of times the health-based guideline.
Chlorine is one of the great public-health achievements of the last century. It keeps municipal water free of the bacteria that used to make people sick, and your utility is right to use it.
It also keeps reacting. As chlorinated water travels through the distribution system, it combines with natural organic matter to form disinfection byproducts — trihalomethanes (TTHMs) and haloacetic acids (HAA5). In the Aquarion Eastern Fairfield County system, TTHMs averaged 64 ppb in 2024, with individual results as high as 87. The federal limit is 80 ppb; the EWG's health-based guideline is 0.15 ppb.
Both numbers are true, and we show them side by side: the water is legally compliant, and it sits far above the level health researchers would prefer for long-term consumption. A peer-reviewed study of a rural system even found these byproducts tend to climb the farther water travels from the plant, and peak in the warm months.
A whole-home carbon filter is built precisely for this — it reduces the byproducts at every tap, not just the kitchen sink.