Cyanide in Drinking Water
EPA limits, health effects, and what to do if your water is affected.
🩨 Health Effects
Short-term exposure above the MCL can cause rapid breathing, tremors, and other nervous system effects. Long-term exposure can cause nerve damage and thyroid problems.
📍 Sources in Water
Enters water from discharge of steel and plastics factories and from fertilizer production. Cyanide is used in gold mining (heap leaching) and can contaminate water near mining sites.
✅ What To Do
Reverse osmosis and chlorination can effectively remove cyanide from water. Activated carbon filters may help. Cyanide violations are uncommon but do occur in industrial areas.
📜 Regulation History
The EPA set the cyanide MCL at 0.2 mg/L (200 ppb) in 1991 under the Phase II rule, measuring free cyanide rather than total cyanide. The WHO guideline is 0.07 mg/L, significantly stricter than the US standard. The regulation targets free cyanide because it is the most toxic form.
🔬 How To Test Your Water
Certified lab tests for cyanide cost $25-$50 and require special sample preservation (sodium hydroxide). Home test kits for cyanide are not widely available. Samples must be analyzed promptly as cyanide can volatilize from water.
💧 Which Filters Remove Cyanide?
Reverse osmosis (NSF/ANSI 58 certified) can reduce cyanide levels. Chlorination at the municipal level converts cyanide to less toxic cyanate. Activated carbon may provide some reduction. Standard home filters are not specifically certified for cyanide removal.
Check your tap water for Cyanide
Search your ZIP code to see if your water system has had Cyanide violations, plus lead testing results and an overall safety grade.
Search your ZIP code →Data from the EPA's Safe Drinking Water Information System (SDWIS). MCLs reflect minimum federal standards; some contaminants may pose health risks below these thresholds.