A red or pink pigmented bacteria known as Serratia marcescens is thought to be the cause of the pink ȁCstuffȁD.
Serratia bacteria are common inhabitants of our environment and can be found in many places,
human and animal feces,
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,
soap and food residues in pet water dishes.
film appears during and after new construction or remodeling activities.
Others have indicated the pink ȁCstuffȁD
occurs during a time of year that their windows are open for the majority of the day.
Reference and further explanation:
Works and Utilities Department/Public Works $!26 Utilities PDFs/pinkdiscoloration.pdf