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A pink film or residue on bathroom and kitchen surfaces generally does not indicate a problem with water quality. In fact, the pink residue is likely a result of airborne bacteria present in the home that produce a pinkish or dark gray film on surfaces that are routinely moist such as toilet bowls, showerheads, sink drains, and tiles. Some people have reported that the pink residue appears in their pet’s water bowl and fortunately it has not caused harm to the pet and is easily cleaned off.
Many experts agree that the bacteria that causes this pink film is most likely Serratia marcesens, a bacteria which is found naturally in soil, food, and in animals. Serratia, which produce a characteristic red pigment, thrive on moisture, dust, and phosphates and need almost nothing to survive. Generally thought to be harmless, recently Serratia marcesens has been tied to urinary tract infections, wound infections, and pneumonia in some people.
The pinkish film often appears during or after construction or remodeling, when dust and dirt containing Serratia bacteria are stirred up. Once the bacteria are airborne, they will seek a moist location where it can proliferate. Some people have reported that the pink residue only appears during certain times of the year, especially when their windows are left open for most of the day. This type of bacteria is present in a number of environments and wind can carry the airborne bacteria or stir up dust in which the bacteria are present.
The appearance of the pink residue can be intensified by the use of activated carbon filters, which remove chlorine from the water. The absence of the normal levels of chlorine in tap water allows Serratia to thrive. Because chlorine naturally dissipates from water that is allowed to collect on surfaces, Serratia may proliferate in these areas.