Don't take a shower. Take a bath.

"Levels of Mycobacterium avium were 100 times higher [in shower heads] than those found in typical household water supplies. M. avium forms a biofilm that clings to the inside of the shower head... [This] might explain why there have been more cases of these lung infections in recent years, linked with people tending to take more showers and fewer baths. Water spurting from shower heads can distribute bacteria-filled droplets that suspend themselves in the air and can easily be inhaled into the deepest parts of the lungs..."