Bathroom

Shower heads can be a breeding ground for bacteria:

http://www.newscientist.com/article/dn17786-shower-heads-make-a-perfect-home-for-bugs.html?DCMP=OTC-rss&nsref=online-news

http://news.bbc.co.uk/1/hi/health/8254206.stm

http://science.slashdot.org/story/09/09/15/1523250/Taking-Showers-Can-Be-Harmful-To-Your-Health?art_pos=2

Mycobacterium avium