There is almost certainly lithium in your water released by the rocks it passed over to reach the dam. Concentrations vary enormously (from 0.1- 600 μg/L) depending on where you live, and a new study reports where there is more lithium, suicide rates are lower.
Lithium salts have been used as a treatment for bipolar disorder since the 19th Century, so it is not altogether surprising its presence in the water supply could offer benefits. On the other hand, even someone with a powerful thirst in a particularly lithium-rich landscape could never get their prescription's-worth out of a tap.
Nevertheless, scientists have considered the possibility of population-wide effects from lithium in drinking water and 15 epidemiological studies have been done comparing regional suicide rates with drinking water concentrations. Professor Anjum Memon of the Brighton and Sussex Medical School has conducted a review of all these studies and found a clearly statistically significant pattern.
In the British Journal of Psychiatry, Memon and co-authors write “Naturally occurring lithium in drinking water may have the potential to reduce the risk of suicide and may possibly help in mood stabilization, particularly in populations with relatively high suicide rates and geographical areas with a greater range of lithium concentration in the drinking water.”
Some of the studies Memon used also found lower crime rates where lithium is abundant, but this aspect was not included in the review, as fewer had tested for this. Despite the same pattern showing up in seven countries, the only way to prove that lithium's environmental presence saves lives is through a randomized trial, adding small doses of the metal to some water supplies and not others, and observing the effects.
Memon suggested this in a statement, proposing targeting “communities (or settings) with demonstrated high prevalence of mental health conditions, violent criminal behavior, chronic substance abuse and risk of suicide.”
Unfortunately, that will not be an easy study to do. For one thing, any effects are unlikely to show up quickly, so local authorities would need a long-term commitment. Moreover, supplementing low levels of natural fluoride in water inspires conspiracy theories that the real agenda is “mind control”. These false claims have been sufficient to see some localities opt to saddle their children with bad teeth. In this context, the addition of an actual psychiatric drug is likely to face an uphill struggle. Historic uses by Native Americans at sacred lithium-rich springs, or the addition to popular soft-drinks, may not be sufficient to overcome these fears.
Moreover, the serious side-effects of lithium medication are real. Most of these are unlikely to occur at the tiny concentrations seen in water, but patients frequently describe the drug suppressing their creativity, something hard to measure if it occurred subtly at a population level. Nevertheless, proposals exist for more targetted fortification and Memon's work suggests low-dosage effects need more research.