Tennessee-American Water pulls water from the Tennessee River, filters the water at its treatment plant on Amnicola Highway, then pipes it out to homes and businesses in downtown Chattanooga and other parts of Hamilton County.
Other areas served by Tennessee-American receive their water from sources other than the river.
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.
The maximum federal limit for average trihalomethane levels in drinking water is 80 parts per billion. For perspective, that's no more than 80 drops of water in an Olympic-sized swimming pool.
The water company report shows the average reading from 33 monitored sites found 76.4 ppb. But those readings ranged from 34.8 ppb to as high as 106.9 ppb.
And the readings are up from levels recorded five years ago. In 2009, second-quarter averages were 59.7 ppb, according to previous reports. In 2012, the figure was 46 ppb.
Hoyos said the Clean Water Act only requires an average reading to meet requirements. But the water company and the state should work to bring all readings below the 80 ppb mark, she said.
"They should be trying to make those standards with every reading," she said.
Daphne Kirksey, spokeswoman for the water company, said residents should not be alarmed by the trihalomethane levels. The 80 ppb limit is based on a yearly average, and of the 33 quarterly samples taken, seven were over 80 ppb.
"Having a result above 80 is not alarming, but we released that for full disclosure," she said.
She added that the company released many other nonrequired readings specifically to inform the public. The company has been creating annual reports for decades -- including 25 years before the reports were federally required.
Additionally, Kirksey said Tennessee-American Water has won the director's award from the Environmental Protection Agency's Partnership for Safe Water for 13 years running.
In fairness, Gary Burriss, an environmental specialist with the Tennessee Department of Environment and Conservation, said regulating trihalomethane levels would be tough because the Tennessee River is a big system. Since it stretches across much of the Southeast, passing numerous cities, towns and forests along the way, there are many inputs for pollution.
"Just being the Tennessee River makes it susceptible to pollution," he said. "Almost all of our systems are moderate or highly susceptible."
Trihalomethanes mostly form when natural organic materials -- such as rotting logs, leaves and dead animals -- interact with chlorine when the water is processed for drinking. That creates higher concentrations of the chemical in the water in the spring and summer and lower concentrations in the cold months, he said.
Overall, public drinking water is safe in Tennessee, Hoyos said. But she said there are further steps government and water utilities could take to make it cleaner, especially when it comes to the chemicals used to clean up the water.
"Some of the products for disinfection can be as nasty as the pollution. There's concern there because they are trying to disinfect it for one thing, but that creates these other compounds that could harm human health in the long run," Hoyos said.
In other words, she said, "You might not get dysentery this week, but you might get cancer six years from now."
Contact staff writer Louie Brogdon at firstname.lastname@example.org or at 423-757-6481.