Electricity generated from falling water

But not in the way you would think. In the setup shown in the video, ordinary water drips from a common reservoir through two bottomless paintcans into two metal wastebaskets. As the process continues, a potential difference of 10-20,000 volts is generated and finally discharged via a spark.

The arrangement is known as a "Kelvin Electrostatic Generator" and would have been the sensation of any reputable alchemist in medieval times. It's still impressive today.

I found the video at the curiously-named and interesting ChocolateChipCookiesRock blog.