Chlorite
ClO₂⁻·Affects lungs, reproductive
The main byproduct of chlorine dioxide disinfection. Regulated by the EPA because of effects on red blood cells and developing infants.
ClO₂⁻
EPA limit
1.0 mg/L (MCL)
Most at risk
Infants, pregnant women, people with hemolytic anemia
Found in
City water
AquaOx filters
YesActivated carbon
What it does to you
Health effects
Chlorite affects red blood cell function. At elevated chronic exposures it can cause hemolytic anemia and methemoglobinemia, where blood loses some of its ability to carry oxygen. Infants are the most sensitive group, and the EPA's 1.0 mg/L MCL is set with infant exposure as the limiting factor.
Animal studies cited in ATSDR's toxicological profile show developmental and neurobehavioral effects at higher doses, which is why pregnant women and households mixing formula are flagged as at-risk. The reproductive system is the secondary concern.
Chlorite is not volatile in the way chlorine or THMs are, so inhalation exposure from showering is not the primary route. Ingestion through drinking and cooking water is what the MCL targets.
Where it comes from
How it gets into your water
Chlorite forms when chlorine dioxide (ClO₂) is used as a disinfectant. Roughly 70% of the ClO₂ a utility doses converts to chlorite during disinfection, so any system using chlorine dioxide will see chlorite in its finished water as well.
Utilities that use ClO₂ are required to monitor both chlorite at the entry point and at distribution sites. Levels are usually under the MCL but can rise if ClO₂ dosing increases (for example to handle a seasonal water-quality challenge).
Chlorine dioxide treatment
Formed as ClO₂ reacts during disinfection
Distribution system
Persists from plant to tap
Tap water
Ingested in drinking and cooking water
Find out for yourself
Is it in your water?
Chlorite only appears in systems that use chlorine dioxide for disinfection. Your annual Consumer Confidence Report (CCR) will list it (and ClO₂) if your utility uses this treatment method. If your CCR doesn't mention chlorine dioxide, chlorite is not in your water.
Where it does appear, the EPA requires reporting if levels exceed 1.0 mg/L at the entry to the distribution system. Utilities tune ClO₂ doses to keep chlorite well below the limit.
The fix
How AquaOx filters it
Activated carbon, especially catalytic carbon, reduces chlorite to chloride during contact. The Centaur catalytic media at the front of every AquaOx system handles chlorite alongside chlorine, chloramine, and chlorine dioxide.
Whole-house filtration protects formula-fed infants and anyone in the household with a sensitivity to oxidizers. Because chlorite ingestion (not inhalation) is the main exposure route, point-of-use filters can also help, but a whole-house system also addresses any oxidizer residuals reaching dishwashers, humidifiers, and ice makers.