A couple of scientists from Wake Forest University noted that water contains trace elements of manganese. That's a metal that occurs in nature, so we're naturally exposed to it all the time; but when it enters the body in higher concentrations than normal, it can cause brain damage. The scientists hypothesized that showers would would aerosolize any manganese in the air and make it inhalable, a particularly effect way of getting the metal into your system.
But doesn't this make humidifiers bad, too? They put water into the air where it can be inhaled. What about fountains and waterfalls? What about fog and rain? We could potentially filter our shower water, but we can't do anything about rain or fog.
And at the beach, the crashing of the waves must put a lot of moisture into the air. Is a day at the beach bad, too? Even with sunscreen?
Everything is bad for us. But worrying is also bad for us. Drat. Where's the lemonade?