Chlorine

Chlorine itself is regulated as a treatment additive, not a contaminant, and the EPA's 4.0 mg/L MRDL is set well above the levels at which acute harm occurs. The bigger concern is chronic, low-dose exposure: chlorine reacts with skin lipids and respiratory tissue, and is associated with worsened eczema, dry skin, brittle hair, and irritation in people with asthma.

In hot showers chlorine vaporizes into the air you breathe and absorbs through the skin. For most adults the dermal and inhalation routes deliver a comparable dose to drinking the same water. This is the exposure pathway pitcher filters cannot address.

The larger long-term issue isn't free chlorine, but what it becomes. Once chlorine reacts with organic matter in source water and inside distribution pipes, it forms trihalomethanes (THMs) and haloacetic acids (HAAs), which are classified as probable human carcinogens and have their own MCLs.

If you are on city water in the US, the answer is almost certainly yes. The exact residual varies by utility and by your distance from the treatment plant. Your municipality publishes the average and range in its annual Consumer Confidence Report (CCR).

Levels tend to be higher in summer when warmer water requires a stronger residual to maintain disinfection through the network. Households at the end of long distribution lines sometimes see lower chlorine but more disinfection byproducts, because chlorine has had more time to react with organic matter on the way.