Most maps of the Twin Cities prominently feature the highways and bridges that connect our region. But few show another grid that is even more crucial to daily life in our modern metropolis.

It just transports poop, not people.

Flush a toilet or take a shower and that water begins a journey — sometimes lasting more than a day — on a network of pipes to be purified at one of nine regional treatment plants. That enormous wastewater system operated by the Metropolitan Council rarely garners much public attention, largely because it works efficiently with few major disruptions.

David Piper wanted to know what happens to all that sewage we produce, specifically in Hennepin County. He asked the Star Tribune about it as part of Curious Minnesota, our community reporting project based on smart questions from inquisitive readers.