Leap onto the slab near the second spout, then climb up to a grip. Leap from the grip to the rod in the serpent head's snout to stop the flow. Climb down using the grips underneath the spout. Grapple on the screw in the center and yank it as you move counter-clockwise (with the Thor statue as 12'o clock) around it. It should screw into the ground, stopping the flow for good and allowing access to a chamber inside the Thor statue.