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.”