Hi,
I have found a mistake in the puzzle in which you have to turn off and on valves to stop water from going out (to the shower in the upper level). Look at these pictures:
All points inside the blue line are connected (there is no obstacle between them) and should therefore have equal water pressure (strictly, at the same height). However, water output 1 (calling 1 to the leftmost output) does not show water flow, and outputs 3 and 4 do show water flow. Try it, in your copy of the game.
I also have to say that this is one of the nicest games I've ever played. Beautiful hand-drawn backgrounds and wonderful music.
Best.