DES MOINES, Iowa (AP) — Residents in major cities downstream from a northwest Iowa tanker car derailment say they’re confident their municipal drinking water is safe even as crews try to contain an estimated 230,000 gallons of oil. Officials in Omaha and Council Bluffs said Monday, they’re monitoring the situation and could switch to well water if oil is detected in the Missouri River, which provides most of their water. But they say they’ve been assured by the Iowa Department of Natural Resources that the oil spilled into the Little Rock River will be contained before reaching the Missouri River.

Others cities, including Sioux City, Iowa, use groundwater and don’t expect problems.