It's a proposal that's no more irrational than the fact that municipalities with naturally occurring lithium in their water don't filter it out -- it has no ill side effects. Unfortunately, given the intense debate over whether or not towns fluoridate their water, it's a proposal that will no doubt meet stiff resistance.
Here's why it's not so crazy. We already live in a world in which we take preventive measures for granted. The law dictates that in motor vehicles, we must wear seat belts and helmets. And doctors regularly prescribe cholesterol-lowering drugs for patients with normal levels of cholesterol, because the practice saves lives.
I realize there is an ideological counter-argument -- government paternalism -- but in aggregate, even ostensibly freedom-loving Americans do not adhere to that standard. Historically, suicide has been illegal, and only three U.S. states have laws allowing a right to die. Cigarettes are taxed heavily and drugs with the potential for abuse are closely regulated. Clearly, we are not comfortable with our fellow human beings engaging in self destruction.
If earlier research is borne out, and doses of lithium far lower than what was previously considered clinically relevant prove to lower suicide rates in a population, and there are no detectable side effects, why, other than paranoia and psychological exceptionalism, wouldn't we put the stuff in the water?