Water sustains life. The same is as true of the ocean as it is in your body or home. Showerheads are often wet and so offer a realm in which life can live. That life can colonize showerheads either from the water itself (tap water contains many kinds of life, from bacteria to nematodes to crustaceans, as does bottled water), or from those organisms that bounce back up onto the showerhead from your body when you stand and cleanse. But one thing that is unique with regard to showerheads compared to those places that Leeuwenhoek studied is that while they are often wet, they are just as often dry. They are the desert washes of your home, places of both bounty and hardship. This mix of soaking wet and bone dry provides circumstances that favor unusual sorts of microbes. When you take a shower these are microbes to which you are exposed, daily. The microbes on your showerhead become airborne as you shower and then fall down onto your body but also into your mouth and nose. As you sing they settle. These settling microbes include both species that are potentially bad news (“pathogens” in the lingo of my tribe such as Legionella which causes Legionnaire’s disease) and those that are potentially beneficial. One group of microbes that fits both of these bills (microbes are almost never simple) is the unusual genus Mycobacterium. Some Mycobacterium are pathogens. Others may be beneficial. Others still are pathogens in some contexts and beneficial in others. This much we know. What we don’t know is why some showerheads seem to be covered in a hairy skin of the stuff and other showerheads (even old, gunky, terrible looking ones of the sort you might find in the hostel of your nightmares) have none. Why? We don’t know. That is what we want to figure out.