Water powered clocks and calculators

[anthomson]

All the new xmas catalogues seem to feature water powered clocks and calculators. Apparently you top them up with tap water approximately once a month, no batteries needed. Are they a gimick or is there a sound scientific principle behind them ?

[McSteve]

I believe they work by having an anode and cathode in the water and current flows between them due to the potential difference. I think one of them is zinc which dissolves but as the clock draws so little power it can last for a ages. It is not really the water that is powering the clock but the chemical reaction. You can also get potato powered clocks as well.

[Bill_lpool]

They could be powered by the fuel cells which are the latest thing in electronics.  Most forms of these are still pretty primitive as its new technology but they plan to use them to power mobile phones, laptops and even cars.  You can now get fuel cells which split water into the gases hydrogen and oxygen out of which the hydrogen is used later in the fuel cell.  Its seems unlikely that they are powered by these tho as i think they would be expensive and combersome?

for more info on fuel cells: http://www.fuelcells.org/basics/how.html