Pink Bacteria
The pink colored film or ring frequently seen on showers, tubs, toilets and pet dishes, is typically caused by growth of the airborne bacteria Serratia marcesens. This harmless nuisance organism reacts with standing water and frequently forms during spring and summer months.
The best treatment for this film is for customers to keep bathroom surfaces clean using chlorine bleach on a regular basis. A small amount of chlorine bleach (three to five tablespoons) added to a normal sized toilet bowl will destroy the bacteria. Whenever a pink film starts to reappear, repeat the cleaning and disinfection process.
Serratia does not survive, and is not present, in the chlorinated drinking water supply.