What are disinfection byproducts?

Disinfection byproducts (DBP) are formed in our distribution system when chlorine used to disinfect drinking water reacts with naturally occurring organic matter in your water.

There are many types of DBP including TTHM (trihalomethane), HAA5 (haloacetic acid), bromate and chlorite.  In all there are 9 types of DBP and 5 are regulated by the North Carolina Department of Environment Quality (DEQ) through rules prescribed by the U.S. Environmental Protection Agency (EPA) under the federal Safe Drinking Water Act.

According to public health officials, the regulations have been established because laboratory animal testing indicates high consumption of some DBP over an extended period of time (equivalent to 20 – 30 years in humans) seems to be associated with a higher risk of some types of liver and kidney cancers in those animals.  However, continued research has shown inconsistent results.  The World Health Organization concluded there is not enough evidence to prove that DBPs are carcinogens, but there is not enough research to classify them as non-carcinogenic. Nonetheless, U.S. EPA has made DBP regulations more stringent several times, most recently in 2012/2013.

Since we use chlorine to disinfect our water, TTHMs and HAA5s may be present. TTHM/HAA5 levels increase over time if the water is not used and also increase as temperatures rise. So, the highest TTHM/HAA5 levels are generally found during the hottest summer months in the parts of the water distribution system that are the farthest distance from the treatment plants, where the water has been in the pipes for the longest amount of time.

It is a constant challenge our staff face. State certified operators continuously monitor water quality to determine the amount of chlorine necessary to inhibit bacteria growth, while limiting the formation of DBP. Staff uses various methods to ensure that your water is disinfected and THM/HAA5 levels are tested throughout the distribution system. Reducing organic carbon prior to disinfection can significantly decrease the level of DBP. Once water has reached the distribution system reducing water age is the best method to reduce DBP numbers, and this is done by flushing water through the pipes via the hydrants.

Results from the 2018 Consumer Confidence Report show that on average DBP were well below the Maximum Contaminant Level (MCL) prescribed by the EPA.


For the full 2018 Consumer confidence Report visit our website.