A USA TODAY motion graphic showing how lead can get into your drinking water.
Ramon Padilla, Karl Gelles and Shannon Green, USA TODAY
About 40,000 Gilbert households received a notice with their July water bills notifying them that the town’s water violated a drinking-water standard set by the U.S. Environmental Protection Agency.
The water contained a higher-than-allowed level of a contaminant called Total Trihalomethanes, or TTHMs, which can increase the risk of cancer and liver, kidney or central nervous system problems if consumed at a high level for many years, according to the agency.
Gilbert’s exposure to the chemical was limited, and residents should not be concerned, according to town staff. A limited amount of the contaminant is not dangerous and is normal in the water supply, they said.
“It’s not an emergency. We are required to notify (residents),” Gilbert water quality supervisor Rebecca Hamel said. “The water is safe to drink.”
The town did recommend that infants, pregnant women, the elderly and people with compromised immune systems consult a doctor for medical advice.
TTHMs are a byproduct of naturally occurring organic material found in water, such as algae or decaying leaves, and chlorine, which is added in small amounts to disinfect the water.
The chlorine is essential to kill viruses that are unsafe for people to consume, Arizona State University professor Paul Westerhoff said. But, like most things in life, there are some consequences, he said.
An individual has a slight risk of getting cancer if exposed to TTHMs at a high level over the course of 60 or 70 years, and “the trade-off is killing pathogens in water that will get you sick … tomorrow,” Westerhoff said.
The EPA maximum level of TTHMs is an annual average of 80 parts per billion. In October, water in northwest Gilbert contained 110 parts per billion because of an equipment failure in one of the town’s water reservoirs, Hamel said.
In April, the water contained 79 parts per billion, which pushed the annual average above 80 parts per billion, Hamel said.
Last month, Tempe also announced it was above the EPA limit, with an annual average of 85 parts per billion.
Westerhoff said he does not believe Gilbert residents should be concerned about the limited increased exposure. He said there is little evidence that these chemicals actually cause cancer.
Additionally, TTHMs are not just in water — they’re consumed in food and inhaled and absorbed in swimming pools and showers.
“The lowest risk is actually drinking the water,” Westerhoff said.
The town is working to decrease the TTHM level to about 50 or 60 parts per billion, which was the town’s average level before the equipment failure, Hamel said.
The town will blend groundwater, which does not contain TTHMs, into the water supply and flush areas of the water system to decrease TTHM levels, in addition to other corrective measures.
The town is awaiting results from its July water-quality test. If the average TTHMs level does not fall back below 80 parts per billion, the town will issue another notice to residents, Hamel said.
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