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Serratia Marcescens

What causes pink staining in my sink, shower, toilet, etc.?
The most likely cause is an airborne bacteria called Serratia Marcescens. This bacteria is common and generally grows in damp conditions such as those found in bathrooms and kitchens.

Serratia produces a pinkish film on surfaces that are regularly moist and subject to humid conditions.  These bacteria particularly thrive in the presence of soap deposits.  They have also been known to grow in pet food bowls.

As a general rule all bacteria needs nutrients for growth and any medium which provides nutrients and moist conditions has the potential for bacterial growth. The film is also commonly found in newly constructed properties or where construction work has been carried out.

What are the factors affecting bacterial growth?
Serratia is an airborne bacteria and can not survive in your chlorinated water supply. These airborne bacteria can come from any number of naturally occurring sources and the condition can be aggravated if you remove chlorine using an activated carbon filter. Serratia can also grow in locations such as toilets in guest bathrooms where the water is left standing long enough for the chlorine disinfectant residual to dissipate.

Favorable Conditions:

  • Damp, humid environments
  • Longstanding water storage (e.g., guest bathroom toilet)
  • Presence of soap, excrement, or food residues


What can I do to prevent this staining?
Once established it is difficult to eradicate the organism entirely. The most effective way of controlling re-growth is regular cleaning with bleach-based cleaning products, paying particular attention to areas where soap products accumulate. The cleaning process is generally more successful if the bleach based cleaning product is allowed to act for a while (about half an hour) before rinsing clean.

Using abrasive cleaning products tends to encourage re-growth as it causes a rough surface to develop where the bacteria can take hold. Often this is why we see Serratia on the grout but not on the tile itself, unless covered in heavy soap deposits/film.

Routine cleaning with bleach-based products, consistent water use (to prevent dissipation of disinfectant residual), and adequate ventilation are the key steps to managing Serratia Marcescens.

AVE MARIA UTILITY COMPANY | 5076 Annunciation Circle, Suite 102, Ave Maria, FL 34142