Disinfection byproducts (DBPs) are chemical compounds that form when chlorine or chloramine reacts with naturally occurring organic matter in water — things like decomposed plant material, algae, and sediment that are present in source water even after treatment. The reaction is unavoidable to some degree: the same process that makes water safe from pathogens also produces these compounds as a side effect.

The two main categories of regulated DBPs are trihalomethanes (THMs) and haloacetic acids (HAAs). Both form through similar pathways but produce different chemical families with somewhat different health profiles. Levels tend to vary seasonally, rising in summer and fall when source water contains more organic material, and can also vary by location within a distribution system.

THMs include chloroform, bromodichloromethane, dibromochloromethane, and bromoform. Of these, chloroform is typically present at the highest concentrations in chlorinated water. The EPA regulates total THMs (TTHMs) with a maximum contaminant level of 80 parts per billion.

Long-term exposure to elevated THM levels has been associated with increased risk of bladder cancer, liver and kidney stress, and potential reproductive effects. THMs are volatile, meaning they can be inhaled during showering or released during dishwashing — so ingestion through drinking isn't the only exposure pathway. Our Clarity and Certainty packages test for the full THM profile using EPA Method 524.2.

HAAs are a less well-known but equally important class of DBPs. The EPA regulates HAA5 — a group of five haloacetic acids — with an MCL of 60 parts per billion. The broader HAA9 group includes four additional compounds that are not individually regulated but are included in comprehensive testing because several of them are considered more potent carcinogens than those in the HAA5 group.

Unlike THMs, HAAs are not volatile — they don't evaporate into shower steam. Ingestion through drinking water is the primary exposure route. Long-term elevated HAA exposure has been linked to increased cancer risk, liver and kidney effects, and potential developmental impacts. Because HAA9 compounds are absent from many standard testing panels, homeowners on municipal water may be unaware of their HAA levels even if they've had their water tested before.

Our Certainty package is the only tier that includes a full HAA9 panel using EPA Method 552.2. For city water customers who want a complete picture of their disinfection byproduct exposure, this is the panel that fills that gap.

Activated carbon filtration is the primary treatment approach for both THMs and HAAs, though effectiveness varies by compound and filter type. THMs are more readily adsorbed by standard activated carbon. HAAs are more challenging — they require higher-quality carbon block filters with adequate contact time to achieve meaningful reduction.

Reverse osmosis systems are effective at reducing both THMs and HAAs and are a good option for point-of-use treatment at the kitchen tap. Whole-home carbon systems can address THM inhalation exposure from showers in addition to reducing ingestion exposure.