Electromagnetism at its most basic level. You can think of electrcity and magnetism as antiperpendicular wave forms that run at 90 angles to each other.
Where electricity flows, so does magnetism. The opposite is also true. The drill works because it has a large magnet, and cheap drills don't usually have advanced circuitry to prevent current from flowing backward if the drill is rotated creating current, instead of current rotating the drill.
You can get these for about $10-$20. The types that run off of a single battery unit or only have a power cord are the easiest to make. Run wires from battery terminals or split the wires to whatever you want to power. Getting one of these is usually easier than trying to create a device, but you can by coiling a wire around a magnet.
It's ideal to store it in some rechargable battery, since it's unlikely to create a constant or sufficient voltage by hand. Chemical sources of power might be less crude and more reliable, but harder to replenish.
Also another way to get pure water is through acid-base neutralization. You'll wind up with some type of salt to filter out, but any acid and any base neutralize into pure water. Hydrochloric acid (a strong acid) and sodium hydroxide (lye) combine to form a solution of table salt in pure water.
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