It seems as if the water-powered gadgets are becoming a bit of a trend. The water-powered green gadgets typically seem to be very low powered and use a small LCD screen. This new water powered calculator has a small re-fillable cartridge that will power the calculator for up to 3 months with just a few drops of water!
It’s a standard calculator, so it lacks the features of the powerful graphical or technical calculators. Since the battery is powered from water, it’s an eco-friendly technology, great for the environment, and doesn’t need any expensive alkaline or lithium batteries.
Source: Coolest-Gadgets