Manganese is dangerous to humans at high levels. Although we are all exposed to small amounts every day, at higher levels manganese is toxic to the nervous system and can lead to a Parkinson's-like disorder. It's already regulated in our drinking water. A new study reveals that we are at risk not just by drinking it but also by inhaling it... in our bath water: A new analysis based on animal studies suggests that showering in manganese-contaminated water for a decade or more could have permanent effects on the nervous system.