The U.S. Environmental Protection Agency (EPA) has set the current maximum contaminant level (MCL) for Total Trihalomethanes (TTHMs) in drinking water at 80 parts per billion (ppb), based on a running annual average. This limit is designed to protect public health by minimizing exposure to these disinfection byproducts.
Current EPA Limit for Total Trihalomethanes (TTHMs)
The EPA regulates TTHMs under the Stage 1 and Stage 2 Disinfectants and Disinfection Byproducts Rules (DBPR). TTHMs are a group of four chemical compounds that can form when disinfectants like chlorine, used to kill harmful germs in drinking water, react with naturally occurring organic matter in the water. Prolonged exposure to high levels of TTHMs has been associated with potential health risks.
Here's a summary of the current TTHM limit:
| Contaminant Group | Maximum Contaminant Level (MCL) | Basis | Regulated Under |
|---|---|---|---|
| Total Trihalomethanes (TTHMs) | 0.080 mg/L (80 ppb) | Running annual average for all samples | DBPR |
Water utilities are required to monitor for TTHMs and report their compliance with this standard to ensure the safety of drinking water.
Historical Context of THM Regulation
The regulation of trihalomethanes has evolved over time as scientific understanding and monitoring capabilities have advanced. Historically, the EPA's initial Total Trihalomethane Rule, finalized in 1979, set an earlier standard. This rule established a maximum allowable annual average level of 100 parts per billion for water systems serving over 10,000 people. Over the years, further research led to the implementation of more stringent regulations, such as the DBPRs, to reduce overall exposure to disinfection byproducts.
Understanding Trihalomethanes
Trihalomethanes are a group of chemicals that include:
- Chloroform
- Bromodichloromethane
- Dibromochloromethane
- Bromoform
These compounds are unintended byproducts of the disinfection process, which is essential for ensuring drinking water is free from dangerous pathogens. The challenge for water systems is to effectively disinfect water while minimizing the formation of these byproducts.
Compliance and Public Health
Water systems serving communities across the United States regularly test their water for TTHM levels to ensure they remain below the 80 ppb MCL. If levels exceed the standard, water utilities must take steps to reduce them, which can include:
- Improving treatment processes to remove more organic matter before disinfection.
- Changing the type of disinfectant used.
- Optimizing disinfectant application points and dosages.
These regulations are crucial for safeguarding public health, balancing the need for effective disinfection with the minimization of potential health risks from byproducts. For more details on drinking water regulations, you can visit the EPA's website on drinking water contaminants.
