Detroit is 82% black. If white and black water customers had not paid their bills at the same rate, and those chosen to be shut off were selected randomly from the group of non-payers, then >80% of those affected would be expected to be black.
In actual fact, it's probable black people are less likely to pay their water bill than white residents.
In Atlanta the Water dept seems to be a place where well-connected blacks can get rich through graft while completely mismanaging the water service and racking up millions in federal fines the taxpayers get stuck with.