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ThinkGeek offers up a nifty little clock, powered solely by water. Using electrolysis or some other polysyllabic term, the clock can run for weeks with nary a refill. It will also run off of any electrolytic fluid so if you want to get a little creative, you're more than free to (hopefully with respect to the potential difficulty of cleaning said clock's reservoir). Perhaps you should just stick to using water.

Catalog Page ($13, in stock) [ThinkGeek via shinyshiny]
See also: Water-Powered Calculator [Gizmodo]