Disinfection Byproducts (THMs and HAAs): What Are They?
How chlorine creates potentially harmful byproducts in tap water.
The tradeoff of disinfection
When chlorine reacts with natural organic matter in water (leaves, soil particles, algae), it forms disinfection byproducts (DBPs). The two regulated categories are trihalomethanes (TTHMs) and haloacetic acids (HAA5). These are associated with increased cancer risk at high, long-term exposure levels. The EPA limits TTHMs to 80 ppb and HAA5 to 60 ppb.
Who has the highest levels
Cities using surface water (rivers, lakes) with high organic content tend to have higher DBP levels, especially in summer when organic matter increases. Southern and southeastern cities with warm surface water sources are often the most affected.
Reducing exposure
Activated carbon filtration (whole-house or point-of-use) effectively removes most DBPs. A whole-house carbon filter treats all water including shower and bath. Point-of-use carbon at the kitchen tap covers drinking and cooking. Boiling water can actually increase DBP concentration by removing water volume while leaving the chemicals behind.