Total Trihalomethanes (TTHM)

The Public Utilities Department (PUD) delivers over 4.4 billion gallons of water to the Athens-Clarke County community.  We rely on source water pulled from the North and Middle Oconee Rivers and the Bear Creek Reservoir.  Your drinking water undergoes over 60,000 tests annually to ensure we provide you with the safe, high-quality drinking water you expect.  

To date, the PUD has met the standards as set by the Environmental Protection Agency (EPA) and Georgia Environmental Protection Division (GA EPD) for all contaminants except one, Total TTHM.  The PUD exceeded the standard at one of our eight sampling sites in September 2021.  

The violation posed no immediate health risk, and if it had, the PUD would have notified customers immediately.  The PUD has taken action to address the issue, and the TTHM results are again below the required levels.  Notification of the above normal levels was mailed to customers, emailed to WaterSmart account holders, posted to social media, at the Water Business Office, and in the local newspaper, and is available here.  

What are TTHMs?

Total Trihalomethanes (TTHM) result when chlorine disinfectants used to treat tap water combine with naturally-occurring organic and inorganic matter present in the water.  Known as a disinfection byproduct, TTHMs are among the substances the Public Utilities Department tests for in our water.  TTHMs are present at low levels in most chlorinated water supplies and can also be present in bottled waters.   

Why do we add disinfectant to our water?

The EPA and GA EPD require public water systems to disinfect drinking water.  Disinfection is a necessary step in our treatment process to eliminate pathogens to prevent illness and protect public health.  The practice of disinfection in the United States has nearly eliminated most acute waterborne diseases, including cholera, typhoid fever, and many other illnesses.

The most widely used type of disinfection in the United States is chlorination.  The Public Utilities Department produces sodium hypochlorite, commonly known as bleach, at the J.G. Beacham Drinking Water Treatment Plant for this purpose.  The disinfectant is added at the end of the treatment process to prevent the growth of bacteria as it travels to homes and businesses across Athens.  

What are the standards for TTHM in my drinking water?

Drinking water standards must meet a Maximum Contaminant Level (MCL) established by the EPA and GA EPD.  The MCLs limit risks to people from chemicals in drinking water. Some MCLs address the daily amount consumed (for chemicals that pose an immediate risk), and others address the amount averaged over a long period of time (for chemicals that pose a long‐term risk).

The MCL for TTHM is 0.080 mg/L, or 80 parts per billion (ppb).  We determine the MCL by calculating the average of four quarterly samples collected at our eight testing locations.     

The PUD exceeded the MCL of 80 ppb for TTHM with a rolling average of 82 ppb at one of our eight sampling sites found on the southeast end of Barnett Shoals Road.

What caused the elevated levels of TTHM?

Levels typically vary within a single water supply depending on the season, water temperature, amount of natural organic matter in the water, pH, amount of chlorine used, time in the distribution system, and other factors.  The Barnett Shoals Road sampling site is at the end of our water distribution system with minimal water usage, possibly contributing to the higher level found in the recent rolling average.

What are the possible health risks of TTHM in my water?

Some people who drink water containing TTHM above the MCL over many years may experience problems with their liver, kidneys, or central nervous system and may have an increased risk of developing certain types of cancer.  Those with a severely compromised immune system, caring for an infant, pregnant, or elderly may be at increased risk.

Research on the connections between Total THM exposures and these health risks is underway. Cancer risks generally accrue over lifetimes and very long periods of exposure. For disinfectant byproducts like TTHM, risks are typically calculated with a daily average of drinking 2 liters of water over a lifetime of 70 years.  

Water that meets the total THMs guideline is considered safe for all domestic uses, including drinking, bathing, showering, and food preparation.  The risk of illness from TTHM is much lower than that of drinking water that has not undergone disinfection.  

What actions is the Public Utilities Department taking to reduce TTHM in our water?

Regardless of the low risks associated with TTHM, the PUD has taken the following actions to address the elevated finding:

  • Increased flushing along sections of our distribution system
  • Installing automatic flushers at strategic points in the system
  • Evaluating process changes to reduce the formation of disinfection byproducts such as TTHM

The results of our November 2021 rolling average are within limits and demonstrate these measures are working to prevent exceeding the MCL in the future.

Where can I get additional information?

The PUD always welcomes the opportunity to answer your questions regarding the safety and quality of your drinking water.  Please reach out to our Drinking Water Superintendent, William Cottrell, at 706-613-3481 or email

Please complete our Report a Water Quality Concern form if you have water quality concerns regarding taste, odor, or color.  

For more information, we recommend the following websites:

We appreciate the trust you place in our water system and will continue to work 24/7 to provide you with excellent water services.