Notice how the floor of the alcove behaves when you turn the crank. Inside the alcove, pull the lever. The only way out is down. You can unscrew the bolts on the drain with your bare hands. You're deep underground and you want to get back up.
Water always flows downhill.
Pay attention in each room to where the water is coming from. Always head upstream, in the direction your hear the water coming from. This is the end of the road. There are several actions you can take here that successfully end the game. Each of them is viable, and some better than others.