When Bond is in the tunnel, a whole bunch of water washes over him. He crawls a little farther and kicks out a screen and jumps down to the floor. The question is, "Where did all the water go?" Because the floor wasn't flooded, so were did it go?
In the James Bond 007 Role Playing Game, they explained this one a little further: Dr. No had set up an endurance/escape course in the tunnels, and the prisoner was expected to break out and be tested against the good doctor's traps. The water was to wash the person down the pipe, into a downward angled pipe, and into the traps. Bond instead braced himself and avoided the water, and then escaped through a vent in the system.
Sounds like made up BS to cover a slipup in the movie, but it did result in a rather cool bit of adventure with all sorts of interesting traps.