When 45 shower heads were tested in homes, 20 percent of them housed significant levels of Mycobacterium avium, bacteria linked to pulmonary disease that most often infects people with weakened immune systems. The pathogens are not only in the water, but they can become suspended in the air so as you breathe, they get drawn deep into your lungs.
Forgoing the showering is obviously not the answer, so what you can do is regularly remove your shower head and thoroughly disinfect it. Also, if your shower head is plastic, switch it out for a metal one since microbes attach more easily to plastic.
I'm definitely going to pass this info onto my gym, since I doubt they ever clean their shower heads. On second thought, I think I'll shower at home from now on. What about you?