Haloacetic Acids (HAA5) in Wisconsin Drinking Water

HAA5 stands for five haloacetic acids: monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid. Like TTHMs, they form when chlorine disinfectant reacts with organic matter in source water. The EPA limit is 60 micrograms per liter as a Locational Running Annual Average. HAA5 and TTHMs are regulated under the same Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBPR), and systems that struggle with one usually struggle with both.

In Wisconsin, the geographic pattern mirrors TTHMs — smaller systems with high-organic source water in northern and southwestern counties see the highest levels. The Driftless Area and Northwoods are particularly affected. Unlike TTHMs, HAA5 is less volatile and doesn't evaporate as readily from hot water, so exposure from showering is lower. The primary exposure route is ingestion.