Looks harmless enough right? Twice I have got sick because of a shower head. The first time was in a hotel in Germany. I didn’t bother to run the water for a minute or two before jumping under the water. Within an hour I knew I had caught a terrible strain of flu. The second time was in my flat in Thailand. I caught conjunctivitis in both eyes which was nasty. It was cured quickly enough with antibiotic eyedrops but when I came back after a few months away the problem started to reoccur. That is when I realised what was going on and installed a new shower head. Problem solved. My advice is to at least wash out your shower head from time to time!