"Lithium is a potent psychiatric drug, one of the primary prescribed medications for bipolar disorder. But it’s also an element that occurs naturally all over the Earth’s crust — including in bodies of water. That means that small quantities of lithium wind up in the tap water you consume every day. Just how much is in the water varies quite a bit from place to place.
Naturally, that made researchers curious: Are places with more lithium in the water healthier, mentally? Do places with more lithium have less depression or bipolar or — most importantly of all — fewer suicides?"