Where are trihalomethanes (THMs) typically found within a water distribution system?

Trihalomethanes (THMs) are typically found in the farthest points from where water enters the distribution system primarily due to their formation during the disinfection process. When chlorine, a common disinfectant, reacts with organic matter in water, it can form byproducts such as THMs. As water travels through the distribution system, these compounds can accumulate, especially at the farthest points from the point of entry or treatment.

In addition to their formation, factors such as longer water residence times in the distribution system can lead to higher concentrations of THMs at these distant points. Water that has been sitting in pipes for longer periods tends to have a higher potential for THM formation, especially if it hasn't been regularly refreshed or circulated.

While THMs can certainly be present throughout the distribution system and may also be found in storage tanks, their concentration is typically highest at these furthest points from the entry where water isn’t circulated or replaced as frequently. This understanding is critical for water quality monitoring and management in water distribution systems.