Chlorite is a byproduct of chlorine dioxide disinfection, and it acts as an oxidizer that can damage an infant's red blood cells. The EPA allows municipal water to carry up to 1,000 ppb (1.0 mg/L) of chlorite under the Stage 1 Disinfection Byproducts Rule, but the health-protective guideline is 50 ppb, based on the California OEHHA public health goal. That is a 20x gap. For a formula-fed newborn, whose entire diet is water-based and whose blood defenses are still immature, that gap is where the risk lives.
One correction worth making up front, because it appears in a lot of writing on this topic. Chlorite is not an ozone byproduct. Ozone disinfection produces bromate. Chlorite forms specifically when a utility uses chlorine dioxide (ClO2) to disinfect the water and control taste, odor, and other byproducts. If your water system runs chlorine dioxide, chlorite comes along with it, and there is no way to disinfect that way without producing some.
For a healthy adult, small amounts of chlorite generally pass through without noticeable harm. A newborn is a different case. Below is what "safe" actually means for chlorite when the person drinking it is a baby, and why the number on your city's compliance report is not the number that protects them.
Legal Limits vs. Health Guidelines for Infant Chlorite Exposure
The EPA legal limit for chlorite is 1,000 ppb, while the OEHHA public health goal is 50 ppb, a 20x difference. The table below compares the federal legal maximum, the independent health guideline, and the CheckYourTap safe level calibrated for newborns. The CheckYourTap figure is the health-protective one, not the legal one.
| Standard | Chlorite Level | Basis |
|---|---|---|
| EPA Maximum Contaminant Level | 1,000 ppb (1.0 mg/L) | Stage 1 DBP Rule, federal law |
| EWG Health Guideline | 50 ppb | Environmental Working Group (adopts the OEHHA PHG, not an independent value) |
| OEHHA Public Health Goal | 50 ppb | California EPA (OEHHA, 2009) |
| CheckYourTap Safe Level (Newborns) | 50 ppb | OEHHA PHG, applied to infants |
The takeaway is simple. Water can be legally compliant with federal law at 1,000 ppb and still hold twenty times the chlorite that health scientists consider protective. The OEHHA public health goal is a health-only figure, set without weighing treatment cost. The EPA legal limit balances health against what utilities can feasibly achieve at scale. Those are different questions, and they produce different numbers.
Where Does Chlorite Actually Come From?
Chlorite comes from chlorine dioxide, one of the disinfectants utilities use to make water microbiologically safe, and roughly 70% of the applied chlorine dioxide converts to chlorite in the finished water (EPA IRIS, 2000). This is worth stating clearly because the common phrasing, calling chlorite an "ozone byproduct," is wrong and points parents toward the wrong test.
Here is the distinction that matters. Ozone (O3) is a different disinfectant, and its main regulated byproduct is bromate, not chlorite. Chlorine dioxide (ClO2) is what generates chlorite, along with a smaller amount of chlorate. So the question to ask your water utility is not "do you use ozone," but "do you use chlorine dioxide, and what are your chlorite levels." Both chlorite and chlorate are regulated as disinfection byproducts, and chlorine dioxide is dosed specifically because it produces fewer of the trihalomethanes that plain chlorine creates. Every disinfection method trades one set of byproducts for another. There is no free version.
Why Are a Newborn's Red Blood Cells So Vulnerable to Chlorite?
Chlorite's documented mechanism is oxidative stress on red blood cells, and newborns are the group least equipped to reverse it because their protective enzymes are still ramping up (ATSDR, 2004). A newborn also drinks roughly 150 mL of water per kilogram of body weight each day, roughly four to five times an adult's intake per kilo (EPA Exposure Factors Handbook, Chapter 3), so the dose per pound is far higher.
Chlorite is a strong oxidizer in the bloodstream. It pushes hemoglobin, the molecule that carries oxygen, toward methemoglobin, a form that cannot bind oxygen well. Adults reverse this constantly using an enzyme called methemoglobin reductase (NADH-cytochrome b5 reductase). In newborns, that enzyme system runs at roughly half of adult capacity for the first few months, and fetal hemoglobin oxidizes more readily. Some infants also have lower reserves of G6PD, another enzyme that protects red cells from oxidative damage. Stack those together and the same oxidative hit an adult shrugs off can, in a baby, translate into methemoglobinemia or hemolytic anemia, meaning red cells that are damaged faster than the body replaces them.
Animal studies on chlorine dioxide and chlorite have also reported effects on early development, including altered neurobehavioral outcomes in rat pups exposed during the newborn window (animal developmental studies reviewed by OEHHA, 2009, and ATSDR, 2004). Those are animal findings, not proof of the same effect in human infants, but they are part of why the health goal sits so far below the legal limit. The prudent reading is that a rapidly developing infant is the wrong body to test a 1,000 ppb limit on.
Does Formula Feeding Raise the Risk?
Yes. For a formula-fed infant, tap water is not an occasional exposure, it is the base of every meal for the first six months, so chlorite in the water becomes chlorite in nearly every feeding. A breastfed baby is buffered by the mother's body; a formula-fed baby drinks the water directly, at that high 150 mL/kg daily rate.
Two common kitchen habits do not help here, and one makes things slightly worse. Boiling water before mixing formula is smart for killing microbes, but it does nothing to chlorite, and because boiling evaporates water, it can nudge the chlorite concentration up rather than down. Standard refrigerator and pitcher filters are built for taste and chlorine, not for inorganic disinfection byproducts like chlorite, so they leave most of it in place. If you want to actually lower chlorite for a bottle, the water needs treatment designed for it, not just heat or a basic carbon cartridge.
What Removes Chlorite From Tap Water?
Reverse osmosis is the most reliable way to remove chlorite, cutting up to 99% of it and bringing typical tap water well below the 50 ppb infant guideline. It works by forcing water through a semi-permeable membrane that blocks the chlorite ion. For families mixing formula, an under-sink RO unit certified to NSF/ANSI Standard 58 is the strongest single choice.
A few other options and where they fit:
- Reverse osmosis (RO) removes up to ~99% of chlorite and most other disinfection byproducts. Because it also strips minerals, keep the rest of the household's calcium and magnesium intake up through diet. Here is what reverse osmosis actually removes.
- Distillation boils water to steam and condenses it, leaving inorganic contaminants like chlorite behind. Very effective, but slow, and it removes minerals too.
- Catalytic carbon is a specialized carbon that can convert some chlorite to harmless chloride. It outperforms standard activated carbon but is less consistent than RO for infant-level targets.
Whatever you choose, the target to hit is the 50 ppb health guideline, not the 1,000 ppb legal ceiling. For more on how disinfectants and their byproducts differ, see our guide to chloramine versus chlorine in city water.
Why We Set a Separate Number for Babies
Most water resources publish one chlorite threshold and apply it to a newborn, a teenager, and a 40-year-old the same way. We don't. CheckYourTap sets the safe level per population group, because an infant with half-strength methemoglobin reductase is not a small adult, and a chemical that an adult clears easily can outpace a baby's defenses. That means doing the work contaminant by contaminant and group by group, including pets, which is slower than repeating a single legal number but a good deal more honest. We generate personalized reports for Connecticut today and are adding states quickly. The guiding standard is what protects a body, not what a regulation permits.
The distance between "meets federal standards" and "safe for my baby" is the whole point. A compliance report answers a legal question at 1,000 ppb. The 50 ppb figure above answers the one that matters for a formula bottle, and a filter at the tap is what closes the gap.
This article is for general information and is not medical advice. Talk to your pediatrician about your specific water source and your baby's feeding, especially if you have concerns about methemoglobinemia or anemia.
Keep Reading
- Is Tap Water Safe During Pregnancy? The Gap Between Legal and Safe
- Arsenic in Well Water While Pregnant: What the Numbers Really Mean
- Reverse Osmosis: What It Actually Removes From Your Water
Sources: OEHHA Public Health Goals (Public Health Goal for Chlorite in Drinking Water, 2009); EPA National Primary Drinking Water Regulations (chlorite MCL, Stage 1 Disinfection Byproducts Rule); EWG Tap Water Database (chlorite health guideline); U.S. EPA (2000), Toxicological Review of Chlorine Dioxide and Chlorite (IRIS); ATSDR (2004), Toxicological Profile for Chlorine Dioxide and Chlorite; animal developmental neurobehavioral findings as reviewed in the OEHHA (2009) Public Health Goal and the ATSDR (2004) Toxicological Profile; EPA Exposure Factors Handbook, Chapter 3 (water ingestion rates).