FAQs • City of San Marcos, TX • CivicEngage

What are TTHMs?: TTHM is an abbreviation for Total Trihalomethanes that form as a by-product during the water treatment process when chlorine reacts with naturally occurring organic matter. The longer the water remains in a pipe, the more of these by-products may be created. For more information please call 512-393-8010.

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Total Trihalomethanes

1. What are TTHMs?: TTHM is an abbreviation for Total Trihalomethanes that form as a by-product during the water treatment process when chlorine reacts with naturally occurring organic matter. The longer the water remains in a pipe, the more of these by-products may be created. For more information please call 512-393-8010.

2. Why is chlorine used as a disinfectant?: Easily considered the most significant public health achievement of the 20th century, chlorine is used to remove waterborne diseases such as typhoid fever and cholera, so that drinking water is safe to consume. The Environmental Protection Agency (EPA) and the Texas Commission on Environmental Quality (TCEQ) require that Public Water Systems use some form of chlorine to disinfect drinking water. Because the risk of waterborne diseases and its effects are much greater than the risk posed by TTHMs, chlorine is still used to disinfect drinking water. For more information please call 512-393-8010.

3. How are TTHMs harmful?: According to TCEQ, some people who drink water containing TTHMs in excess of the maximum contaminant level over many years may experience problems with their liver, kidneys, or central nervous system, and may have an increased risk of getting cancer. For more information please call 512-393-8010.

4. What is the Maximum Contaminant Level for TTHMs?: Maximum Contaminant Level (MCL) is highest permissible level of a regulated contaminant. The MCL for TTHMs is 0.080 milligrams per liter (mg/L). This means that 1 mg/L is equivalent to 1 part per million (1 part per million would be equal to 1 penny out of $10,000). For more information please call 512-393-8010.

5. Is the water safe to drink?: Yes! At no time was the City’s water unsafe to drink. This is not a public health emergency. There is no need to seek an alternative water supply. You do not need to boil your water or take other precautions before consuming City Water. There are no known short term acute impacts who have consumed water that has exceeded the MCL. If you have health concerns, you should seek the advice of a physician. For more information please call 512-393-8010.

6. Was everyone affected?: No. Out of a total of 8 sites that were sampled and only 1 site, an isolated part of the system, exceeded the MCL. For more information please call 512-393-8010.

7. What has the City done?: In the short-term the City will increase flushing of the pipes in the area affected. City Staff in conjunction with the Guadalupe-Blanco River Authority and a consulting firm are investigating improvements for reducing TTHMs. Funding for the recommended improvements will be requested in the Fiscal Year 2017 Water and Wastewater Budget. For more information please call 512-393-8010.