Interesting Vox article about how studies have shown that "places with higher levels of trace lithium had lower suicide rates." The effects are significant. "High-lithium areas have suicide rates 50 to 60% lower than those of low-lithium areas."
Lithium is a powerful psychiatric drug found naturally on the Earth's crust and in bodies of water. This means that we consume small amounts of lithium in our water today; just how much depends on the location.
“In general, in the United States, lithium levels are much higher in the Northeast and East Coast and very low in the Mountain West... And suicide rates track that exactly — much lower suicide rates in the Northeast, and the highest rates of suicide are in the Mountain West.”
A number of prominent psychiatrists are making the claim that "we could save tens of thousands of lives a year with a very simple, low-cost intervention: putting small amounts of lithium, amounts likely too small to have significant side effects, into our drinking water, the way we put fluoride in to protect our teeth." This is a controversial topic to consider as putting supplemental lithium into water "would be a concerted effort by the government to put mind-altering chemicals in the water supply to change the behavior of the citizenry." If it works, it could be a great idea, but preventing suicide isn't just about the chemicals; it's about changing one's thought patterns as well.