When my D was at college it went down a bit, but not by much because S was still home and he eats a lot. When S was at college, it went down more because D was out of the house too, so I was just buying for the two of us. That said, I wouldn’t say our expenses went down when our kids were in college, because we were paying tuition and room and board for them. And that wasn’t cheap!
As far as heating and water and power, really didn’t make much difference…