In Mission: Impossible - Rogue Nation, Ethan Hunt must switch access cards in an underwater chamber. There is a large intake with gallons upon gallons of water flowing down it constantly, but no mention of an outlet for all that water. The only exit seems to be a closed hatch. Where was all that water going?
They were in a power station, and the water was flowing through a turbine. If you recall, when the "flood gates" at the top were opened, the water began circulating and Hunt had to start swimming against that current. The water would flow through the grate at the bottom of that chamber.