What is Chlorite and Why Does It Matter?

Chlorite is a chemical byproduct, not something utilities add to water on purpose. It forms when chlorine dioxide — a disinfectant used to kill bacteria and viruses — breaks down inside the water supply. Utilities often choose chlorine dioxide because it's effective and produces fewer harmful byproducts than traditional chlorine. But the tradeoff is chlorite. Once chlorine dioxide does its job, chlorite is left behind in the water that reaches your tap.

The health concerns around chlorite are real, especially for vulnerable groups. At elevated levels, chlorite can damage red blood cells, reducing their ability to carry oxygen — a condition called hemolytic anemia (EPA). Infants, young children, and pregnant women face the greatest risk. The nervous system may also be affected with long-term exposure. Even at moderate levels, some research suggests chlorite can cause fatigue, weakness, and developmental concerns in children (EWG). These aren't worst-case scenarios — they're documented effects tied to the kind of exposure levels showing up in real water systems right now.

The EPA's legal limit for chlorite is 1,000 parts per billion (ppb) in drinking water. That sounds protective, but the Environmental Working Group (EWG) sets its health guideline much lower — at just 210 ppb — based on the most current health research. The gap between those two numbers matters. Across 356 water systems tested, the average chlorite level was 306 ppb. That's above the EWG guideline, even if it technically stays under the EPA limit. More striking: 319 out of 356 systems — nearly 90% — exceeded the EWG health guideline. The highest recorded level reached 2,410 ppb, more than 11 times the EWG threshold. Staying within a legal limit doesn't always mean staying within a safe one.

Chlorite contamination follows a clear geographic pattern tied to which utilities use chlorine dioxide as their primary disinfectant. Texas leads the country with 105 affected systems — far ahead of any other state. Oklahoma (30 systems), Colorado (29), Alabama (29), and Missouri (17) round out the top five. These states share a mix of older infrastructure, larger surface water systems, and treatment plants that rely heavily on chlorine dioxide. Surface water sources like rivers and reservoirs tend to carry more organic matter, which pushes utilities toward stronger disinfectants like chlorine dioxide. That's a reasonable choice for killing pathogens — but it also means more chlorite in the finished water.

The good news is that chlorite is very effectively removed at the point of use, meaning right in your home. Reverse osmosis (RO) filtration removes up to 99% of chlorite from drinking water. An activated carbon filter can also reduce chlorite levels significantly, though RO systems offer the most consistent protection. If you're in Texas, Oklahoma, Colorado, Alabama, or Missouri — or anywhere that uses chlorine dioxide treatment — it's worth testing your tap water first to understand your actual exposure. Echo Water's systems use multi-stage filtration, including reverse osmosis, specifically designed to address disinfection byproducts like chlorite. Knowing what's in your water is the first step. Filtering it out is the straightforward next one.

Regulatory Standards for Chlorite

Cities With the Highest Chlorite Levels

States Most Affected by Chlorite

Frequently Asked Questions

Related Contaminant Guides