Total Trihalomethanes (TTHMs) in Drinking Water

🩨 Health Effects

TTHMs form when chlorine reacts with naturally occurring organic matter in water. Long-term exposure is linked to increased risk of bladder cancer, and some studies associate high levels with reproductive problems and miscarriage risk.

📍 Sources in Water

TTHMs are not found in nature; they are created during the water treatment process. Levels are higher in surface water systems and in summer months when organic matter and water temperatures are highest.

✅ What To Do

Activated carbon filters (NSF/ANSI 53 certified) and reverse osmosis reduce TTHMs. Refrigerating water in an open pitcher can also help dissipate them. Boiling water does not remove TTHMs and may concentrate them.

📜 Regulation History

The EPA first regulated TTHMs in 1979 at 0.10 mg/L. The Stage 1 Disinfectants and Disinfection Byproducts Rule (1998) lowered the MCL to 0.080 mg/L as a running annual average. The Stage 2 D/DBP Rule (2006) required compliance at each individual monitoring location rather than as a system-wide average. The WHO guideline for chloroform (the primary THM) is 0.3 mg/L.

🔬 How To Test Your Water

Certified lab tests for TTHMs cost $50-$150 due to the specialized volatile organic analysis required. Home test kits for TTHMs are available for $20-$40 but are less precise. Levels vary seasonally, so testing in summer gives the highest readings. Your utility reports TTHM levels in the annual Consumer Confidence Report.

💧 Which Filters Remove Total Trihalomethanes (TTHMs)?

Activated carbon filters (NSF/ANSI 53 certified for THM reduction) are the most practical and affordable option. Granular activated carbon (GAC) and carbon block filters both work well. Reverse osmosis systems also reduce TTHMs. Look specifically for NSF/ANSI 53 certification for TTHM reduction on the filter label.

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