The Michigan Department of Environmental Quality is responsible to ensure that public water supplies are in compliance with the federal and state Safe Drinking Water Acts. This includes ensuring that the water is tested and safe to drink, approving any new source of water, approving any changes in the chemical treatment of potable water, conducting annual inspections and review of the water supply, and approving most significant engineering and design additions and alterations to the supply.
I suspect that most Water Departments have their own lab to do frequent testing.
Guess you got me. No state monitoring if the locals are not doing their job.