Disinfection byproducts in drinking water
Disinfection byproducts form inside the water system itself. The chlorine or ozone added to drinking water to kill the organisms that cause waterborne disease reacts with the natural organic matter already in the source water — and, where that water carries bromide, with bromide — and the products of that reaction travel to the tap with the water. 9 of them are covered here.
They are not measured one at a time on a water report. The four trihalomethanes are summed and reported as total trihalomethanes (TTHM), and five haloacetic acids are summed and reported as HAA5, so the figure on a consumer confidence report is usually a total rather than any one compound below.
The 9 in this group
Each page answers the same questions for its own contaminant: where it has been recorded, what the limit is, and what removes it — with the source for every answer.
Bromodichloromethane
Bromodichloromethane (BDCM) is one of the four trihalomethanes regulated as part of TTHM (limit 80 ppb). It forms when source water contains bromide. Its EPA health goal (MCLG) is zero.
Dichloroacetic Acid (DCA)
Dichloroacetic acid is one of the five haloacetic acids in HAA5 (group limit 60 ppb). Its EPA health goal (MCLG) is zero.
Bromoform
Bromoform is the fully brominated trihalomethane, regulated as part of TTHM (limit 80 ppb) and most common where source water is high in bromide. Its EPA health goal (MCLG) is zero.
Trichloroacetic Acid (TCA)
Trichloroacetic acid is one of the five haloacetic acids in HAA5 (group limit 60 ppb). Its EPA health goal (MCLG) is 0.02 mg/L.
Chloroform
Chloroform is the most common trihalomethane and the surrogate the NSF/ANSI 53 VOC test uses for the family. It is regulated as part of total trihalomethanes (TTHM limit 80 ppb). Its EPA health goal (MCLG) is 0.07 mg/L.
Total THMs
Total trihalomethanes (TTHM) are the sum of four byproducts — chloroform, bromodichloromethane, dibromochloromethane, and bromoform — formed when chlorine reacts with organic matter. The EPA limits TTHM to 80 ppb (0.080 mg/L).
EPA MCL 0.08 mg/L
Dibromochloromethane
Dibromochloromethane (DBCM) is one of the four trihalomethanes regulated as part of TTHM (limit 80 ppb), favored when source water contains bromide. Its EPA health goal (MCLG) is 0.06 mg/L.
Bromate
Bromate forms when ozone disinfection reacts with naturally occurring bromide in source water. The EPA limits bromate to 10 ppb (0.010 mg/L), with a health goal (MCLG) of zero.
EPA MCL 0.01 mg/L
Total Haloacetic Acids (HAA5)
HAA5 is the sum of five haloacetic acids formed when chlorine reacts with organic matter. Unlike trihalomethanes they are non-volatile, so they are an ingestion concern rather than a shower concern. The EPA limits HAA5 to 60 ppb (0.060 mg/L).
EPA MCL 0.06 mg/L
Which limits are enforceable
3 of the 9 carry an enforceable EPA limit of their own — a maximum contaminant level (MCL) a public water system must meet: Total THMs, Bromate and Total Haloacetic Acids (HAA5).
The other 6 carry an EPA health goal (MCLG) but no enforceable limit of their own. A health goal is the level below which there is no known or expected risk to health; it is not a level a water system is required to meet. Each page states its own figure: Bromodichloromethane, Dichloroacetic Acid (DCA), Bromoform, Trichloroacetic Acid (TCA), Chloroform and Dibromochloromethane.
What removes a contaminant, which certification covers it, and what boiling does to it are answered by name on each page above, with the source for each answer.
Where they come from
- Byproduct of disinfecting drinking water with chlorine
- Formed when chlorine reacts with natural organic matter such as decaying leaves, runoff, and algae
- Elevated when the source water contains naturally occurring bromide
- Levels are highest in warm-season surface water
- Byproduct of disinfecting drinking water with ozone
Collected from the source list each contaminant page publishes, where each line is attributed.
Is it in your water?
Each page above lists the water systems that reported a result above the health guideline for that contaminant. To start from a place instead of from a compound, look your system up directly.
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