Here's a slick new video that showcases a very old concept. In 1867, Lord Kelvin found a way to generate sparks (and a surprisingly high voltage) using twin showers of water. This video will show you why it works — as well as why it doesn't work quite well enough.
The folks at Veritasium have a cool video that shows us how two showers of water, manipulated just right, can generate a massive voltage. It's called Lord Kelvin's thunderstorm or, for the less poetic among us, Lord Kelvin's water dropper.
By crosslinking containers and coils, we can essentially create a bucket full of negative charges and a bucket full of positive charges. But perhaps "full" is too generous a term. About only one in 10,000,000 water molecules is ionized. When the machine sparks, there are relatively few electrons moving from one side to the other.
We see the sparks between the buckets below, but we don't see the current flowing through the water above. The charged positive coil forces negative charges down and positive charges up through the stream. The negative coil does the same, in reverse. So there's a low, continuous current through the water above, which sporadically creates a spark of current between the balls below.