Re: Water used as a power source

Dear User,

The answer is very simple - galvanic potential, named after Luigi Galvani 
who first demonstrated it using an infamous frog's leg. It is the same 
principle which drives the "lemon battery" -- an often used school example. 
 
http://www.physics.odu.edu/htmlstuf/physicspage/lemon.htm 

http://www.energy.ca.gov/education/projects/projects-html/lemon.html

Two metals which are in contact with an electrolyte solution can generate 
enough electricity to drive a small device, in this case a clock. Tap water 
is far from pure and contains enough ions to serve as electrolyte. If you'd 
put distilled water in the reservoirs, the clock would not work very well, 
as the only electrolyte in solution would be carbon dioxide/carbonic acid. 
If you noticed, you have two galvanic pairs in sequence, in order to 
increase voltage 
(you have copper - - -zinc-copper- - -zinc arrangement)
These two pairs should generate ~2.0 V potential, with a very small 
current.

Hope it helps.

A.G.E.