Minneapolis in Minnesota uses mussels as well which is what Tom is talking about. But it’s to monitor the overall river quality and not just the drinking water. The DNR in Minnesota also uses bio-monitoring in depth for tracking quality in lakes. <br>To look this up, search Minneapolis MN water treatment mussels.,(reply>), I'm from Duluth, I didn't even know that. I'll have to look that up,(reply>), AMAZIN!,(reply>), Thanks for the additional info! As a Minneapolis resident, I had no idea we did this, but I will absolutely be adding this fun fact to my repertoire!