Do you know of any quantitative data about lead in typical filament after extrusion? Could you also post some of the links were you got your infos from?
In earlier days when we had lead pipes for water, the problem of lead poisoning would actually arise when the water sat for an extended period in the pipes and had the time to acquire higher concentrations of lead. (Faucets made from lead containing brass were actually made until the late 80s).
My guess would be, that due to the little contact time the filament and the brass actually have, there isn't much mass transfer taking place. So the concentration of lead in the final plastic product should be in the ppm range at max? The concentration of lead in the water will be even lower, probably by orders of magnitude? What is in the filament originally (flexibilizers, etc) is probably a lot worse.