Chlorine
Cl₂·Affects skin,, lungs
The disinfectant most US utilities add to kill pathogens. Effective at its job, but it doesn't stop reacting once it leaves the treatment plant.
Cl₂
EPA limit
4.0 mg/L (MRDL)
Most at risk
People with sensitive skin, asthmatics, frequent shower users, infants
Found in
City water
AquaOx filters
YesCentaur catalytic carbon
What it does to you
Health effects
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.
Where it comes from
How it gets into your water
Chlorine is intentionally added by water utilities as the primary disinfectant. Most US municipal systems use free chlorine (gas or hypochlorite) at the plant, then maintain a residual of roughly 0.2 to 2.0 mg/L throughout the distribution network so the water stays disinfected on its way to your tap.
The residual is the part you smell and taste. It is by design: the EPA requires utilities to maintain a detectable residual so water doesn't sit unprotected in mains and service lines.
Municipal treatment plants
Primary disinfection at the plant
Distribution residual
Maintained throughout the network
Hot showers
Vaporizes into bathroom air
Tap water
Direct ingestion
Find out for yourself
Is it in your water?
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.
The fix
How AquaOx filters it
Chlorine is filtered by chemical reaction with catalytic carbon. The Centaur catalytic carbon at the core of AquaOx pulls chlorine out of solution as water passes through, dropping the residual to non-detect levels in independent testing.
Because AquaOx is whole-house, it filters chlorine from your shower water too. The shower is where most people get the largest single dose of chlorine each day: hot vapor, open pores, deep breaths. Pitcher filters do not address this.