In which areas should you monitor for high total trihalomethanes (TTHM) levels?

Monitoring for high total trihalomethanes (TTHM) levels is particularly important in areas with the highest water age. TTHMs are a group of disinfection byproducts that form when chlorine used in the water treatment process reacts with organic matter in the water. In locations where water has a longer residence time—typically referred to as high water age—there is more opportunity for these reactions to occur. As the water sits in the distribution system, organic materials can accumulate, and as a result, the concentration of TTHMs can increase.

In contrast, low water flow areas may not necessarily correlate with higher TTHM levels due to potential variations in water quality and turnover. Regularly turned over storage tanks are generally more effective in reducing TTHM concentrations because the water is continually refreshed. Likewise, high traffic water lines might experience more disturbance and might not have the same accumulation of organic materials leading to TTHM formation. Thus, focusing on areas with the highest water age is critical for effective monitoring and management of TTHM levels in drinking water systems.