Chlorine Dioxide in Drinking Water

🩨 Health Effects

Short-term exposure above the MCL can cause nervous system effects and anemia in infants and young children. Chlorine dioxide and its byproduct chlorite are regulated because of these concerns.

📍 Sources in Water

Chlorine dioxide is used as an alternative disinfectant, particularly by systems that want to avoid TTHM and HAA5 formation. It is generated on-site at treatment plants.

✅ What To Do

If your utility has a chlorine dioxide violation, contact them for details. Reverse osmosis can reduce chlorine dioxide and its byproducts. Such violations are uncommon and typically indicate a dosing problem at the treatment plant.

📜 Regulation History

The EPA set the maximum residual disinfectant level (MRDL) for chlorine dioxide at 0.8 mg/L in 1998 under the Stage 1 D/DBP Rule. Its byproduct chlorite has an MCL of 1.0 mg/L. The WHO guideline for chlorine dioxide is also 0.8 mg/L, consistent with the US standard.

🔬 How To Test Your Water

Testing for chlorine dioxide requires specialized amperometric or colorimetric methods, typically costing $25-$50 at a certified lab. Home test kits for chlorine dioxide are available but less common than those for free chlorine. Your utility monitors and reports chlorine dioxide levels if they use it as a disinfectant.

💧 Which Filters Remove Chlorine Dioxide?

Activated carbon filters can reduce chlorine dioxide and its byproduct chlorite. Reverse osmosis (NSF/ANSI 58 certified) also removes chlorine dioxide residuals. Standard carbon filters (NSF/ANSI 42 certified) are generally effective since chlorine dioxide reacts with carbon similarly to free chlorine.

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