I am vehemently opposed to drugging people without their consent -- particularly when the delivery vehicle for the drug is water. To add drugs to the water is to violate every citizen's bodily integrity and their basic right to offer or withhold consent to medical treatment (you may say that people can choose to filter it or buy bottled water, but plenty of people can't afford to do that.)
Additionally, you could be putting people at risk for serious health problems. Lithium may have benefits for some or even most, but it can cause problems for others -- it can, for example, interact with other medications and even foods (like grapefruit/grapefruit juice) in dangerous ways. Even without drug and food interactions, it would be impossible to regulate individual dosages because people don't all drink the same amounts of water, and water that's been boiled for any significant period of time will have higher concentrations of lithium (like if someone fills a large kettle in the morning, and then brings it to a boil several times throughout the day for individual cups of tea, or in homemade broth...basically the more water evaporates, the higher the dose of lithium per cup of water, because the lithium would not turn into vapor with the water -- it would stay in the kettle or the pot).
(And you may ask, then, if I'm opposed to fluoridating water, and my answer is yes; I drink the fluoridated water in my city and I think it's probably harmless to me, but that doesn't change my position on this issue -- I think it's wrong to drug people without their individual consent (and just because fluoride and lithium are naturally occuring doesn't change my opinion that, when used in carefully calculated amounts for a specific medical purpose, they qualify as "drugs"....or, perhaps it would be better for me to say that I am opposed to forcing healthcare interventions on people, preventative or otherwise, whether using naturally occuring or synthetic substances.))
