Total trihalomethanes (TTHM) in Tap Water
TTHMs are disinfection by-products that form when chlorine reacts with natural organic matter in water. They are the trade-off of effective disinfection.
Formed in-system when chlorine disinfectant reacts with organic material.
- 1Chlorination of water with organic matter
A result is read with its context
Reported from utility and state compliance monitoring, typically as a running annual average. PurityMap publishes this substance per water system on individual system and city-report pages, where the source dataset provides a value.
- Above reference
- Evidence exceeds a reference level.
- Detected
- This substance was found in the monitoring record. Being present is not the same as being above a reference level, and this signal does not say which.
- Not detected
- Somebody looked and the laboratory reported nothing above its reporting limit. This is a result, and it is not the same as nobody looking.
- Not monitored
- No sampling for this substance has been reported for this system. Nothing is known either way, and an empty row is not a clean one.
59 cities where total trihalomethanes (TTHM) was detected
- AllentownPA→
- AmarilloTX→
- AshevilleNC→
- AtlantaGA→
- AustinTX→
- BethlehemPA→
- BiloxiMS→
- BoiseID→
- BostonMA→
- BuffaloNY→
- CaryNC→
- CharlotteNC→
- ChattanoogaTN→
- ChicagoIL→
- ClevelandOH→
- DallasTX→
- DenverCO→
- DurhamNC→
Showing 18 of 59. Open a state for its full list. The scope of PurityMap’s record, not a national prevalence estimate.
What can carry a total trihalomethanes (TTHM) reduction claim
- Activated carbon
Highly porous adsorption media targeting chlorine, disinfection byproducts, volatile organic compounds, and organic chemicals.
- Reverse osmosis
Semi-permeable membrane separation removing dissolved minerals, heavy metals, and persistent fluorinated chemicals down to 0.0001 microns.
Boiling does not remove a dissolved chemical compound and can concentrate it. Many pitcher and refrigerator filters carry no verified claim for a compound like this at all.
A finding establishes the need, the need names the capability, the capability requires a verified certification. No product appears before that sequence completes. Filter Finder →
Frequently asked
Answers cite the same records as the page. How PurityMap analyzes water data
TTHMs are disinfection by-products that form when chlorine reacts with natural organic matter in water. They are the trade-off of effective disinfection.
The enforceable federal limit is 80 µg/L (MCL). The published health benchmark reads: 80 µg/L federal limit (MCL). PurityMap reads every measurement against its stated benchmark and never sets its own.
Chlorination of water with organic matter.
Long-term exposure above the limit is associated in studies with bladder-cancer risk and possible reproductive effects. Disinfection remains essential; the goal is to minimize by-products, not to stop disinfecting.
Treatment technologies commonly certified to reduce Total trihalomethanes (TTHM) include Activated carbon, Reverse osmosis. Match the exact certified claim to your water before buying. Holding a format is not the same as holding the claim.
In PurityMap's published record, Total trihalomethanes (TTHM) was detected in 59 cities (of 59 with a result) across 26 states. This is the scope of our record, not a national prevalence estimate.