-by Silas Allen, originally published on October 6, 2014

DUNCAN — If you’re spending time in Duncan soon, consider packing bottled water.

Officials notified residents that the city’s drinking water had violated federal purity standards. City officials say the problem is the result of a prolonged drought that has left city reservoirs several feet below normal.

Results of water quality tests in Duncan between July 2013 and July 2014 showed elevated levels of trihalomethanes, a type of contaminant that appears as a byproduct when water is chlorinated. Although the contaminant levels exceeded standards set by the federal Environmental Protection Agency, the city’s water is safe to drink for most people, said Scott Vaughn, the city’s public works director.

“You don’t need to boil the water, for instance,” Vaughn said. “It was not and is not an immediate health concern.”

Some people who drink water with elevated levels of trihalomethanes for many years could develop liver, kidney or central nervous system problems, according to the EPA. Drinking water with high levels of trihalomethanes every day for decades also could cause a slight risk of cancer, the agency reports.

Although the immediate risk is small, Duncan city officials advised elderly residents, those with severely weakened immune systems and parents of infants to consult a doctor about possible health effects.

Vaughn said the problem is because of a serious drought that has gripped Stephens County for the past four years. Duncan averages about 38 inches of rain per year, according to the Oklahoma Climatological Survey. But the city’s total rainfall has fallen below that average for several years, the survey reports.

In 2011 and 2012, the city received about 15 inches of rain for the entire year — less than half of what it could expect to receive in a typical year.

Although the city has fared somewhat better since then, the rainfall hasn’t been enough to make up for the damage that was done in 2011 and 2012, Vaughn said. Waurika Lake, the city’s primary source of drinking water, stands about 32 percent of its normal capacity. As water levels plummeted, water quality suffered, Vaughn said, leading to the increased levels of trihalomethanes.

Another part of the problem stems, ironically, from the success of the city’s water conservation efforts. As reservoir levels dropped, city officials implemented water conservation measures. The city is under Stage 4 water restrictions, which limit outdoor watering to one day a week.