Pink water usually comes from one of two sources: a bacterium that thrives on moisture and leaves a visible pink film, or a chemical used in water treatment that can temporarily tint your supply. The cause depends on where you’re seeing the color and whether it appears as a stain on surfaces or as a tint in the water itself.
Pink Film on Surfaces: Bacterial Growth
The most common cause of pink discoloration in bathrooms, kitchens, and toilets is a bacterium called Serratia marcescens. It produces a pink-to-reddish pigment and grows readily in any moist environment. You’ll typically see it as a slimy film around shower drains, on grout lines, along the waterline of toilet bowls, and around faucet bases. Many people mistake it for mold, but it’s bacterial.
Serratia marcescens doesn’t actually come from your water supply. It’s an airborne organism that lands on wet surfaces and colonizes them. It feeds on fatty residues from soap, shampoo, and body oils, which is why bathrooms are its favorite habitat. Anywhere water sits or surfaces stay damp for extended periods gives the bacterium what it needs to multiply and produce that distinctive pink color.
This bacterium is generally harmless for healthy people who encounter it on household surfaces. It can, however, cause infections in people with weakened immune systems, particularly if it enters open wounds or the urinary tract. For most households, the concern is cosmetic rather than medical.
Pink Tap Water: Treatment Chemicals
If the water flowing from your faucet has an actual pink or pinkish-purple tint, the likely culprit is potassium permanganate. Water utilities use this oxidizing chemical to remove dissolved iron and manganese from the supply. It works by converting dissolved iron into solid particles that can be filtered out, and it does the same for manganese.
When applied correctly, potassium permanganate gives water a faint pink tint that disappears before it reaches your tap. But if too much is added, or if something goes wrong with the treatment process, that pink color can make it all the way through the system. The EPA notes that maintaining a permanganate residual in the distribution system is undesirable specifically because of its tendency to give water a pink color.
Pink water from treatment chemicals is typically a short-lived event. Utilities monitor these levels and correct the dosing quickly once the discoloration is reported. If your tap water suddenly turns pink, contact your water provider. They can confirm whether a permanganate overfeed occurred and advise you on when the water will run clear again.
Pink Water in Swimming Pools
Pools can develop their own version of pink water, caused by what’s commonly called “pink algae.” Despite the name, it’s actually a type of bacteria rather than true algae. It appears as pink or reddish streaks on pool walls, in corners, and around fittings where circulation is poor. Standard chlorine levels often aren’t enough to eliminate it because the bacterial colonies form a protective slime layer that resists normal sanitizer concentrations.
Treating pink algae requires super-chlorination (shocking the pool to very high chlorine levels) combined with a product specifically designed for this type of bacteria. The combination forces the chlorine into its strongest oxidizing form, which can penetrate the slime layer and kill the colonies beneath it.
How to Tell the Causes Apart
Where and how the pink appears tells you what’s going on. A pink film that builds up on surfaces over days or weeks, especially in humid rooms, points to Serratia marcescens. Pink water coming directly from the tap suggests a water treatment issue. And pink streaks in a pool that resist normal chlorine are almost certainly bacterial colonization.
Iron bacteria in well water can sometimes cause confusion, but they produce a different color profile: yellow, orange, red, or brown stains, often with an oily rainbow sheen on standing water and rusty, filamentous slime. If you’re on a private well and seeing true pink rather than rust-colored staining, Serratia marcescens on your fixtures is the more likely explanation.
Removing Pink Stains and Preventing Them
For bathroom surfaces, a 1:1 solution of household bleach and warm water is effective. Spray it on the affected area, let it sit for 10 minutes, scrub, and rinse thoroughly. Dry all surfaces with a clean towel afterward, because eliminating moisture is the real key to prevention. Serratia marcescens will return to any surface that stays consistently wet, no matter how well you clean it.
Practical steps to keep it from coming back include running the bathroom exhaust fan during and after showers, wiping down wet surfaces, and fixing any dripping faucets or leaky fixtures. Squeegee-ing shower walls after each use makes a noticeable difference. The bacterium can’t colonize surfaces that dry out between uses.
For pink tap water caused by potassium permanganate, running your cold water tap for several minutes can help flush the discolored water through. The EPA sets a secondary standard of 15 color units for drinking water, which is a non-enforceable guideline based on aesthetics rather than health risk. If pink water from your tap persists beyond a day, your water utility should be investigating the cause.