What are THMs?

THMs are a group of chemicals that are created when water is chlorinated. When drinking water is disinfected with chlorine, the chlorine mixes with organic material, that is naturally present in the water (such as leaf debris), and creates other chemicals called “disinfection by-products (DBPs).” THMs are one of the by-products of chlorinating water. There are four different trihalomethanes: bromoform, chloroform, bromodichloromethane, and chlorodibromomethane. Together they are called “total trihalomethanes” or TTHMs. The amount of TTHMs in drinking water can change, depending on such things as water temperature, the amount of chlorine needed to disinfect the water, the time that the chlorine interacts with the organics, and even the amount of  organic material present in the groundwater.

IWSD tests for TTHM’s in the drinking water.  Previously, a running annual average of 100 parts per billion (ppb), was allowable.  EPA lowered this level to 80 parts per billion in January 2004. For the third quarter of 2006 the District had an annual average levels of  around 16.60 ppb.  This is under the MCL of 80 ppb.  In addition, the District is under the MCL for HAA5s (Haloacetic Acids).  The maximum allowable level for HAA5s is  60 ppb, and for the third quarter of 2006, our levels were at 11.80 ppb.

The Immokalee Water & Sewer District  made the switch in November 2005, from free chlorine to chloramines as a disinfectant, to reduce the concentrations of TTHMs and HAA5s in the finished water. Since the change in disinfection, the levels have to continued to drop.