Yes, it is an interesting thing but not really fulled by water as such. The fuel is really the meterials making up the anode and cathode which means it's just energy storage via refined metals. What you said in the other post was interesting about the urine battery. Unfortunatly this is just using the urine and a poor electrolyte and wasting metals.
I would like to see a 'real' urine battery that only uses the urine itself and not any of the electrode materials inside.