Byrd..as your up in Northern Minnesota and using water from a municipal well you have some of the best in the country,i would not put anything in it..i assume your not around iron country and the well is down into rock where you getting ground water that's been there since the glacier moved back 11,000 years ago.
the town of Buhl,which is up north,has been selling it's city water for years as "pure not purified".i would just watch out for your storage from freezing unless you have good containers with room for the ice to expand.i don't see any problem with a cement floor.also your at the top of the watershed and your not getting "used" water.