Reference one of the questions:
In the late 60's fluidics based control systems were available as kits to colleges and universitys. Admittedly the one's I knew about were based on air rather than water but other mediums should work too. The individual logic units were approx 25x12x8 and the connecting 'wires' were plastic tubes approx 6mm dia (from dim memory). The standard logic units nand, nor etc. were available and yes, even power amplification.
The units I saw were controlling 5/6 axis automatic milling machines within a test production line. There was a rumour (unsubstantiated) that the military were trying to develop this for aircraft control systems as they would supposedly be proof against EMP.
Successful as this was I don't think that the logic gates could be miniaturized to the same degree as semiconductors.
Now if the experiments, to create logic gates with light ever work on a microscopic scale, bear fruition we might all be looking at a different scenario.