Messing around with the basement to Highrise had me discovering an isolated patch of invisible water on the floor. I can jump in it and make splashes and noises. It's not a gigantic problem, but it does mess with item placement a little. I don't know if this is the only water patch there, but it's the only one I've noticed so far.
Attached a picture of the ripples around my character, and the location relative to the elevator.