There are only 24 hours in a day, so how it is possible to eliminate 28 liters in 24 hours without exceeding 1 liter per hour?
Try this: weight yourself before and after sleep.
Yes, the statement is about kidneys. It is only about kidneys, though, and includes all of the information.
No, it has nothing to do with breathing or any other method of eliminating water. The statement says that kidneys max out at 1.0 liters per hour, and 28 liters per day. One of those 2 is obviously wrong, unless we aren't talking about Earth.