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Facts About Serratia marcescens: The Pink Stuff in Your Toilet, Shower, or Sink



Every few years, a customer will call the Notla Water Authority Drinking Water Laboratory to ask about a slimy pink substance that sometimes forms in moist areas around their homes. They most frequently observe it in toilet bowls, on surfaces in shower stalls and bathtub enclosures, on tiles, in sinks, and in pet water dishes.




The most common cause of this pink “stuff” is a red- or pink-pigmented bacteria known as Serratia marcescens. Serratia bacteria are common inhabitants of our environment and can be found in many places, including human and animal feces, dust, soil, and in surface waters. The bacteria will grow in any moist locations where phosphorus containing materials or fatty substances accumulate. Sources of these substances include soap residues in bathing areas, feces in toilets, and soap and food residues in pet water dishes. The conditions for the survival of Serratia marcescens are minimal, and the bacteria may even feed upon itself in the absence of other nutrients. The pinkish film often appears during and after new construction or remodeling activities. Others have indicated the pink “stuff’ occurs during a time of year that their windows are open the majority of the day. This problem also more commonly occurs in humid regions of the country.


These airborne bacteria can come from any number of naturally occurring sources, and the condition can be further aggravated if customers remove the chlorine from their water with an activated carbon filter. In recent years, the popularity of home water filtration systems has grown tremendously, and the presence of Serratia has appeared more and more frequently in homes which remove the chlorine disinfection from the water supply. Serratia can also grow in tap water in locations such as toilets in guest bathrooms where the water is left standing long enough for the chlorine residual disinfectant to dissipate. Serratia will not survive in chlorinated drinking water.


Serratia marcescens is not known to cause any waterborne diseases. Members of the Serratia genus were once known as harmless organisms that produced a characteristic red pigment. More recently, Serratia marcescens has been found to be pathogenic to a small percentage of people, having been identified as a cause of urinary tract infections, wound infections, and pneumonia in hospital environments.


Once established, the organism usually cannot be eliminated entirely. However, periodic and thorough cleaning of the surfaces where the pink slime occurs, followed by disinfection with chlorine bleach, appears to the best way to control it. Avoid abrasive cleaning agents as they may scratch bathroom and kitchen fixtures, which will make them even more susceptible to bacteria. As the porous walls of a toilet tank can harbor many opportunistic organisms, a few tablespoons of chlorine bleach can be periodically stirred into the toilet tank and flushed into the bowl itself to keep a disinfectant residual in the standing water at all times.


* From the American Water Works Association, Opflow Article: Question of the Month, page 3. November 2000

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