The alarm was raised after field tests on tap water in the town of Hugo, population 720, returned positive results.

The contamination has so far been traced to a single well where further investigations are taking place.

Locals have been told to use bottled water until the cause has been pinned down.

Capt. Michael Yowell of Lincoln County Sheriff’s Office said they were trying to determine that it “isn’t because of the field test kit - that it isn’t a false positive”.

Hugo Mayor Tom Lee said: “We’ll figure it out.”

He added: “It just blew my mind.”