The pink or salmon film that appears in a shower corner, a toilet bowl, a pet bowl or around a drain is almost always a bacterium that lives in the air, Serratia marcescens. It settles onto damp surfaces and feeds on soap, shampoo and food residue. It arrives from the room, not from the pipe, which is why buying a water filter to stop it is money wasted.
Why it turns up where it turns up
Look at the places it appears: the grout line where shampoo runs down, the waterline of a bowl that is rarely flushed, the rim of a pet dish, the seal of a shower door. All of them are permanently damp and all of them carry a food source. It thrives in humid bathrooms and is more visible in summer or after a spell of humid weather. It does not appear inside a sealed water heater or in a closed pressure tank, because the organism needs air and residue to get going.
Getting rid of it and keeping it away
Clean the affected surface with a chlorine bleach based cleaner, let it sit long enough to work rather than wiping straight away, and scrub the grout and the seals rather than just the porcelain. Then attack the conditions: run the extractor fan or open a window after showers, squeegee the glass, dry the pet bowl daily rather than topping it up, and flush guest bathrooms that sit unused. Removing the moisture and the residue is what stops it coming back within a fortnight.
When the water is genuinely part of the story
Municipal supplies carry a disinfectant residual, and the film shows up faster where that residual is low by the time water reaches the fixture, or on an untreated well with no disinfection at all. You can read what your utility reports, since every community water system publishes an annual Consumer Confidence Report and the EPA maintains a finder for it. Do not confuse this with orange or black staining, which is iron or manganese; our sulfur removal from well water page covers those well problems.
Questions people ask about pink residue from water
Is the pink residue dangerous?
For healthy people it is usually a nuisance rather than a hazard, but it should not be left on surfaces used for food or on pet bowls, and immunocompromised households should be more careful.
Will a whole-house filter stop pink film forming?
No. The organism arrives through the air and grows on soap residue in damp places, so filtering the incoming water does nothing about it.
Why did the pink stains only start recently?
Common triggers are a more humid season, a fan that has stopped working, a change in cleaning products, or a bathroom that has fallen out of daily use.