Total trihalomethanes (TTHM) in drinking water
Also called TTHM, Trihalomethanes, THMs, Chloroform, Bromodichloromethane, Dibromochloromethane, Bromoform.
- Legal limit
- 80 ppb
- Health goal
- None
Values in parts per billion (ppb). Forms or is added in treatment.
Where the rules stand
Final MCL of 80 ppb (0.080 mg/L) for four trihalomethanes combined: chloroform, bromodichloromethane, dibromochloromethane and bromoform. EPA sets no health goal for the group as a whole.
What EPA says about health
EPA lists liver, kidney or central nervous system problems and an increased risk of cancer from long-term exposure above the MCL.
Where it comes from
EPA calls TTHM a byproduct of drinking water disinfection. NSF describes it as a byproduct of chlorination.
What handles it
- NSF/ANSI 53
Claim to look for: Trihalomethanes (TTHM) Reduction
Also listed as: VOC Reduction
NSF listing wording. WQA wording: "TTHM (as chloroform)."
NSF listing footnotes say the VOC claim includes TTHM. WQA wording: "VOC (as chloroform)."
- NSF/ANSI 58
Claim to look for: Trihalomethanes (TTHM) Reduction
NSF listing wording for reverse osmosis systems.
Filters with that claim on a certifier’s listing
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PUR PLUS Faucet Filtration System, Horizontal (PFM400H)
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Brita Elite Water Filter Faucet System (SAFF-100/FF-100)
Faucet mount
Aquasana Claryum Direct Connect (AQ-MF-1)
Under-sink carbon
AquaTru Classic (AT2000)
Countertop reverse osmosis
Sources
- National Primary Drinking Water Regulations, U.S. EPA. Checked Oct. 4, 2026.
- 40 CFR 141.2 Definitions (HAA5 and TTHM), eCFR. Checked Oct. 4, 2026.
- Search for NSF Certified Drinking Water Treatment Units (standards and reduction claims lists), NSF. Checked Oct. 4, 2026.
- NSF listings for the NSF/ANSI 53 "VOC Reduction" claim (footnote lists included chemicals), NSF. Checked Oct. 4, 2026.
- Contaminant Reduction Claims Guide, NSF. Checked Oct. 4, 2026.
- Find WQA Certified Products (Gold Seal listings by standard and claim), Water Quality Association. Checked Oct. 4, 2026.
- SDWA Dataset Download Summary (codes from SDWA_REF_CODE_VALUES.csv, 2026 Q2 extract), U.S. EPA ECHO. Checked Oct. 4, 2026.