Why Do I Have Pink/Gray Stains on My Fixtures?
What Causes Pink Residue
Pink residue is generally not a problem with water quality. In fact, pink residue is likely a result of airborne bacteria which produce a pinkish or dark gray film on regularly moist surfaces. Such surfaces include toilet bowls, shower heads, sink drains, and tiles.
Some people have also noted that the pink residue appears in their pet's water bowl, which causes no apparent harm to the pet and is easily cleaned off.
About the Bacteria
Many experts agree that the bacteria that causes these pink stains is most likely Serratia marcescens, 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.
What Makes it Worse
The pinkish film often appears during or after construction or remodeling, when dust and dirt containing Serratia bacteria are stirred up. Once the bacteria is airborne, it will seek a moist location in which it can grow. Some people have reported that the pink residue only appears during certain times of the year, when their windows are left open for most of the day. This bacteria is present in a number of environments and wind can carry the airborne bacteria or stir up dust in which the bacteria is present.
The use of activated carbon filters, which remove chlorine from the water, can make the problem worse. The absence of the normal levels of chlorine in tap water allows Serratia to thrive.
Getting Rid of the Pink Residue
The best solution to this problem is to continually clean the involved surfaces to keep them free from bacteria. Compounds containing chlorine work best, but keep in mind that abrasive cleaners may scratch fixtures, making them more susceptible to bacterial growth.
Chlorine bleach can be used periodically to disinfect the toilet and help to eliminate the occurrence of the pink residue. An easy way to do this is to stir three to five tablespoons of fresh bleach to the toilet tank, flush the toilet to allow the bowl to be disinfected, and add another dose of bleach to the tank as it is refilling. The use of toilet "cakes" containing disinfectant can help keep the problem under control. By keeping bathtubs and sinks wiped down and dry, the formation of pink residue can be avoided.