EPA legal limit
80 ppb
Maximum Contaminant Level
EWG health guideline
0.15 ppb
Science-based, stricter target
IARC classification
Group 2A (bromodichloromethane) / Group 3 (chloroform)
Cancer research classification
Health effects
Long-term exposure above health guidelines is associated with increased cancer risk (bladder cancer in particular), and epidemiological studies have linked elevated TTHM exposure during pregnancy with small-for-gestational-age outcomes, preterm birth, and spontaneous pregnancy loss. The EPA MCL of 80 ppb is set at 533× the EWG health guideline of 0.15 ppb.
Where it comes from
TTHMs are not found naturally in source water. They are formed during the water treatment process when chlorine (used to kill bacteria and viruses) reacts with decaying leaves, algae, and other organic matter. Higher levels are typically found in utilities drawing from surface water sources such as rivers and reservoirs.
How it's regulated
Regulated by EPA under the Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR). The MCL is 80 ppb as a running annual average. The EWG health guideline of 0.15 ppb is based on a one-in-one-million cancer risk level. Many utilities comply with the EPA limit while exceeding the science-based health guideline by a wide margin.
The EPA vs EWG gap
The legal limit (80 ppb) is 533× higher than the EWG health guideline (0.15 ppb). Water can be legally compliant while still exceeding the science-based threshold.
How to filter total trihalomethanes
Not all filters address total trihalomethanes. Look for independently certified filters — NSF International certification means the removal claim has been independently verified.
Important nuance: the FC1 filter in the Kangen K8 removes bromoform — one of the four TTHM compounds. However, the other three (chloroform, bromodichloromethane, dibromochloromethane) are not removed by the FC1. The TTHM total as regulated can therefore still exceed guidelines even with a Kangen machine in use. For full TTHM reduction, an NSF 53 certified activated carbon block filter or reverse osmosis is required. The Kangen machine addresses part of the TTHM picture — be specific about which compound, not the category.
Frequently asked questions
What is total trihalomethanes?
A group of four chemical compounds — chloroform, bromodichloromethane, dibromochloromethane, and bromoform — formed when chlorine reacts with naturally occurring organic matter in source water.
What are the health effects of total trihalomethanes?
Long-term exposure above health guidelines is associated with increased cancer risk (bladder cancer in particular), and epidemiological studies have linked elevated TTHM exposure during pregnancy with small-for-gestational-age outcomes, preterm birth, and spontaneous pregnancy loss. The EPA MCL of 80 ppb is set at 533× the EWG health guideline of 0.15 ppb.
Is total trihalomethanes regulated in drinking water?
Regulated by EPA under the Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR). The MCL is 80 ppb as a running annual average. The EWG health guideline of 0.15 ppb is based on a one-in-one-million cancer risk level. Many utilities comply with the EPA limit while exceeding the science-based health guideline by a wide margin.
Where does total trihalomethanes come from?
TTHMs are not found naturally in source water. They are formed during the water treatment process when chlorine (used to kill bacteria and viruses) reacts with decaying leaves, algae, and other organic matter. Higher levels are typically found in utilities drawing from surface water sources such as rivers and reservoirs.
How do I remove total trihalomethanes from tap water?
The most effective methods for removing total trihalomethanes are: Activated carbon block filter, NSF 53 certified filter, Reverse osmosis (RO), NSF 58 certified RO system, Whole-home carbon filter. Look for NSF-certified systems — independent certification confirms removal claims have been verified.
Is total trihalomethanes in your water?
Enter your ZIP code to see the measured level in your specific utility.