The state of Colorado has officially determined that surface water is mixing in with the city of Ouray’s drinking water, leading to changes that are likely to affect the water’s smell and taste and force the city to spend millions of dollars for a long-term fix.

The Department of Public Health and Environment notified the city earlier this month it has reclassified Weehawken Spring from groundwater to groundwater under the direct influence of surface water.

State health officials required the ...