Disinfection Byproducts
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.
Substance identity
- Scientific name
- Trihalomethanes
- Family
- Disinfection Byproducts
- CAS number
- Not published
This guide explains the compound. Only a water-system record or household test can tell you whether it appears in your water.
- Federal reference
- 80 µg/L (MCL)Enforceable maximum contaminant level
- Health-based goal
- 80 µg/L federal limit (MCL)US EPA Stage 2 Disinfectants and Disinfection Byproducts Rule
- Measurement context
- Stated in the recordReported 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.
- Cities on record
- 1US cities in PurityMap's published record where Total trihalomethanes (TTHM) appears
A reference is a published threshold, not a safety line drawn by PurityMap. Where a result sits against it is a finding; whether that constitutes a violation is a separately published compliance field.
What is Total trihalomethanes (TTHM)?
TTHMs are disinfection by-products that form when chlorine reacts with natural organic matter in water. They are the trade-off of effective disinfection.
Where Total trihalomethanes (TTHM) comes from
Formed in-system when chlorine disinfectant reacts with organic material.
- Chlorination of water with organic matter
How Total trihalomethanes (TTHM) is measured
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.
Why context mattersHow PurityMap reads a Total trihalomethanes (TTHM) result
Evidence exceeds a reference level. Used sparingly and only when warranted.
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.
Somebody looked and the laboratory reported nothing above its reporting limit. This is a result, and it is not the same as nobody looking.
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.
Where the numbers come from
- A laboratory result for one sampling point
Collected under a monitoring programme, analysed by an approved method, and reported with its own detection limits.
- Read against a published reference
The reference comes from the regulator, with its own effective date. PurityMap does not set thresholds and does not adjust them.
- Attached to a system's Water Profile
Where it contributes to the published assessment alongside the evidence quality of the record it came from.
The full evidence chain →
Where Total trihalomethanes (TTHM) is found across the U.S.
These are the places in PurityMap’s published record where Total trihalomethanes (TTHM) appears on a water system’s monitoring results. It reflects the systems and sampling we track, not a national prevalence estimate.
Treatment capability, if a finding establishes a need
The formats that commonly hold a verified reduction claim for Total trihalomethanes (TTHM) are Activated carbon, Reverse osmosis. Holding the format is not holding the claim — the certification record is what is checked.
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.
Whether a system-level measurement or a household-tap measurement is the relevant scope depends on how the compound enters the water — a published characteristic of the record, not an assumption drawn here.
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 questions
What is Total trihalomethanes (TTHM)?
TTHMs are disinfection by-products that form when chlorine reacts with natural organic matter in water. They are the trade-off of effective disinfection.
What is the limit for Total trihalomethanes (TTHM) in drinking water?
The enforceable federal limit is 80 µg/L (MCL). The health-based goal is 80 µg/L federal limit (MCL). PurityMap reads every measurement against its stated benchmark and never sets its own.
Where does Total trihalomethanes (TTHM) in tap water come from?
Chlorination of water with organic matter.
Why does Total trihalomethanes (TTHM) 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.
How do you remove Total trihalomethanes (TTHM) from water?
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.
Where is Total trihalomethanes (TTHM) found in the US?
In PurityMap's published record, Total trihalomethanes (TTHM) appears in 1 city across 1 state. This is the scope of our record, not a national prevalence estimate.
Sources and methodology
Reference values on this page come from the governed contaminant record. Local occurrence claims stay on the linked water-system evidence pages, where sampling scope, period and source remain visible.
How PurityMap analyzes water data →