Tennessee-American Water Co. is touting straight A's on its annual drinking water quality report for Chattanooga. But a clean water group laments that "good enough for government work" doesn't cut it for residents.

According to readings from the water company's 2013 report, Chattanooga's drinking water passes federal requirements on all nine monitored substances and two disinfection byproducts. The company also disclosed levels on 13 other substances it is not required to report, such as alkalinity, aluminum, potassium and others.

But the readings for one type of carcinogenic chemicals -- trihalomethanes -- are too high for comfort, according to Tennessee Clean Water Network Executive Director Renee Hoyos.

Trihalomethanes are made when chlorine disinfects organic material in the water that is pulled from the Tennessee River. Long-term exposure to high levels of these chemicals can harm the liver, kidneys and central nervous system -- and may cause an increased risk for cancer, according to the report.

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