What is the “pink stuff” that can sometimes be found in your sinks, showers, and toilets?
 
The most common cause of this pink "stuff" is a red or pink pigmented bacteria known as Serratia marcescens. Serratia bacteria can be found in many places, including human and animal feces, dust, soil, and in surface waters. The bacteria will grow in any moist location where phosphorous 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.
 
These airborne bacteria can be made worse by removing chlorine 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 using chlorine filtration.
 
Serratia marcescens is not known to cause any waterborne diseases. More recently, Serratia marcescens has been found to effect a small percentage of people, causing 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, can help control it.

To clean pet water dishes, bathrooms, and kitchen surfaces

• ‍Scrub the surfaces where phosphorous and fatty substances or the bacteria accumulate with a brush and a household cleanser.
• Disinfect the surfaces where the slime has formed with a strong chlorine bleach solution. 
• Leave the disinfectant solution on the affected surface(s) for 10 – 20 minutes before thoroughly rinsing away with clean water.
• ‍Use care with abrasives to avoid scratching the fixtures, which will make them even more susceptible to the bacteria.

To control Serratia marcescens in toilets

• Clean the bowl thoroughly and spray chlorine bleach into the bowl and under the bowl rim.
• Also add 1/4 cup of bleach to the toilet tank.
• Let the bleach stand for 15 – 20 minutes.
• The bleach should not be left in the toilet tank for prolonged periods; it will damage the rubber valves and seals inside.
• Whenever a pink film starts to reappear, repeat the cleaning and disinfection process.

Cleaning and flushing with chlorine will not necessarily eliminate the problem but will help to control these bacteria. Keep bathtubs and sinks wiped down and dry, and use a cleaning solution that contains chlorine to curtail the onset of the bacteria.

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