Lithium was the original "up" ingredient in 7-UP soda

Greek physicians thousands of years earlier were treating mental disorders with mineral water now thought to be high in lithium.

when lithium does work, it is a wonderful thing. Suicidal depression and mood swings relieved within the week. To this day, lithium is one of the few medications proven to decrease the risk of suicide.

When rats are given lithium-laced or lithium-free food for 6 weeks, the lithium-dosed rats had less arachidonic acid, and more 17-OH DHA, which is an anti-inflammatory metabolite of the fish oil, DHA. 17-OH DHA seems to inhibit all sorts of inflammatory proteins in the brain.

Interestingly enough, lithium has been shown to be the only effective drug (at least to slow the progression down) in another inflammatory, progressive, and invariably fatal neurotoxic disease, ALS, which is also known as Lou Gerhig's disease (2), and lithium is being studied in HIV, dementia and Alzheimer's disease.

Seems that counties with higher lithium levels in the water had a statistically significant decrease in the incidence of homicide, suicide, arrests for opiates and cocaine, and violent criminal behavior. Now to put things into perspective, a high lithium water content translates to about 2mg of lithium a day. Pharmacologic psychiatric doses typically start at 300mg daily.

Furthermore, lithium has been found to [improve] distractibility... and produce improvement of selective attention to stimuli... it prevents behavioral alterations owing to social isolation, lowers [aggressive behavior] owing to confinement...and causes a normalization of spontaneous motor activity.

In another paper studying lithium in the Japanese water supply, human longevity increased with the amount of trace lithium in the water.

the addition of a bit of lithium to the matrix will decrease the overall sodium gradient in the brain, decreasing neuroxicity, and increasing the efficiency of brain energetics. From the Japanese drinking water, lithium, and suicide study:
"It can be speculated that very low but very long lithium exposure can enhance neurotrophic factors, neuroprotective factors and/or neurogenesis."

On the negative side, Swedish researchers tested thyroid effects of trace lithium in the water in some villages in the Peruvian Andes. Some of these villages had some 10-20X the natural lithium in the food and water of the Japanese subjects, up to a maximum of 30mg daily (which is, of course, within an order of magnitude of the pharmacologic dose of 300mg).  They found that lithium in the water seemed to decrease active thyroid hormone levels and increase thyroid stimulating levels—lithium as a medicine will tend to cause hypothyroidism.

side effects: lithium is toxic to the thyroid and kidneys (and heart in high amounts), causes weight gain, is fatal in overdose