How to get rid of Serratia marcescens in drinking water fixtures

September 22, 2025 •

4 min read

While often mistaken for a waterborne issue, the pinkish slime of Serratia marcescens is typically caused by an airborne bacterium that thrives in moist, not flowing, water. This guide will explain how to get rid of Serratia marcescens in drinking water fixtures and other household surfaces.

Quick Summary

To eliminate Serratia marcescens, focus on regular and thorough disinfection of moist surfaces like toilets and sinks using a chlorine bleach solution. Improve ventilation to reduce ambient moisture and prevent the bacteria's return, as it's airborne and feeds on soap scum.

Key Points

It's Airborne, Not Waterborne: The bacteria primarily spreads through the air, colonizing moist surfaces rather than contaminating the water supply itself.
Clean with Chlorine: Regular disinfection with a bleach-based solution is the most effective method for controlling pink slime growth on surfaces.
Ventilate and Dry Surfaces: Reducing humidity and keeping surfaces like sinks and showers dry are critical preventive measures.
Be Aware of Carbon Filters: Activated carbon filters can increase the risk of growth by removing chlorine, a key disinfectant.
Low Risk for Healthy Individuals: While a concern in hospital settings, Serratia marcescens poses little threat to healthy people at home.
Regular Maintenance is Key: Because the bacteria is so common, consistent cleaning and prevention are more effective than one-time eradication efforts.

Understanding the Pink Culprit: Serratia marcescens

Despite its alarmingly red or pink appearance, the bacterial film commonly found in bathrooms is usually caused by Serratia marcescens, a naturally occurring airborne bacterium. This microorganism produces a reddish-orange pigment called prodigiosin, which gives the slime its characteristic hue. It is crucial to understand that in residential settings, this is typically a surface-level problem, not an indication of your drinking water being systemically contaminated. The bacteria travel through the air and settle on damp surfaces, feeding on phosphorous-rich materials and fatty substances found in soap scum, shampoo residue, and mineral deposits.

Why Your Water System May Worsen the Problem

Though Serratia marcescens is not a waterborne disease in typical circumstances, certain water systems can inadvertently create an ideal environment for its growth. The primary factor is the use of activated carbon filters, which are very popular for improving the taste and odor of tap water. While effective for those purposes, these filters remove chlorine, which is a key disinfectant used by municipal water supplies to inhibit bacterial growth. When the residual chlorine is gone, standing water in toilet bowls, shower heads, or pet dishes becomes a hospitable environment for airborne Serratia to colonize and form biofilms.

Step-by-Step Cleaning and Disinfection

Eradicating established Serratia marcescens requires consistent and thorough cleaning. Here is a guide to tackling the pink slime in different areas of your home.

For Toilets and Tubs:

Preparation: Put on rubber gloves and ensure the area is well-ventilated by opening a window or turning on a fan.
Scrub: Use a brush and an abrasive household cleanser to scrub the visible pink slime from the toilet bowl, rim, and any affected surfaces in your tub or sink. For hard-to-reach areas, a mixture of baking soda and dish soap can be effective.
Disinfect: For toilets, add about 1/4 cup of chlorine bleach to the tank. Spray or wipe a chlorine bleach solution (diluted as per manufacturer's instructions) onto all cleaned surfaces in the tub and sink area.
Wait: Let the disinfectant sit for 15–20 minutes to effectively kill the bacteria.
Rinse Thoroughly: Flush the toilet several times to rinse the bleach from the tank and bowl. Thoroughly rinse all other surfaces with clean water.
Repeat: Repeat this process whenever the pink film reappears. Do not leave bleach in the toilet tank for prolonged periods, as it can damage the rubber parts.

For Pet Water Dishes and Other Small Items:

Wash: Scrub the item with hot, soapy water to remove any visible biofilm.
Disinfect: Use a diluted bleach solution (one teaspoon of bleach per gallon of water) to soak the item for a few minutes.
Rinse Completely: Rinse the item thoroughly with fresh water to remove all traces of bleach before allowing pets to use it again.

Advanced Prevention Strategies

Elimination is difficult, but management is key. By minimizing moisture and removing the bacteria's food sources, you can significantly reduce its recurrence.

Improve Ventilation: Use exhaust fans during and after showers for at least 30 minutes to reduce humidity. If your bathroom lacks adequate ventilation, consider installing an exhaust fan or using a dehumidifier.
Wipe Down Surfaces: Get in the habit of wiping down sinks, tubs, and showers after each use. Keeping surfaces dry removes the moist environment Serratia needs to flourish.
Address Standing Water: Regularly flush out toilet bowls, especially in guest bathrooms that see infrequent use, to prevent chlorine dissipation.
Control Soap Scum: Use products that reduce soap scum buildup, as this is a primary food source for the bacteria.

Comparison: Surface Cleaning vs. Water Treatment for Serratia marcescens


Feature	Surface Cleaning (Bleach, Scrubbing)	Water Treatment (RO, Filters)
Effectiveness	High, directly eliminates visible biofilms on surfaces.	Limited, as Serratia is airborne and colonizes surfaces, not the water supply itself.
Application	Targeted to specific areas where pink slime is visible.	Affects all water entering the home; may create conditions for Serratia growth if it removes chlorine.
Cost	Low, uses common household cleaners.	Higher initial and maintenance costs for equipment.
Primary Goal	Control the aesthetic nuisance and surface bacteria.	Improve taste, remove contaminants, soften water (though can increase Serratia risk by removing chlorine).

Health Considerations for Serratia marcescens

For the average, healthy person, the presence of Serratia marcescens is generally harmless and primarily an aesthetic nuisance. However, in hospital settings, it can cause more serious, opportunistic infections, particularly for individuals with compromised immune systems, the elderly, or infants. For these vulnerable populations, exposure to the bacteria can lead to conditions like urinary tract infections, wound infections, and pneumonia. If you have immunocompromised family members, heightened vigilance with cleaning is essential. For more information on infectious diseases, consult a reliable source like the Centers for Disease Control and Prevention.

When to Consider Professional Help and Testing

If you have concerns about the presence of Serratia marcescens beyond the typical bathroom slime, such as recurring infections in vulnerable individuals, you may want to have your water tested by a certified laboratory. This is particularly relevant if you have a private well. For persistent water quality issues unrelated to Serratia, a water treatment professional can help you assess and address the problem. A professional can identify underlying issues and recommend appropriate solutions like system disinfection, but for the pink slime itself, diligent surface cleaning is the best course of action.

Conclusion

Successfully managing Serratia marcescens means understanding its airborne nature and focusing on consistent surface disinfection rather than attempting to treat the drinking water itself. By adopting a routine of thorough cleaning with chlorine-based products, coupled with effective ventilation and moisture control, you can effectively combat the pink slime and maintain a healthier home environment. Remember that total eradication is challenging, but with regular maintenance, control is well within your reach.

Frequently Asked Questions

The pink or reddish-orange residue, often mistaken for mold, is most likely a bacterial biofilm caused by Serratia marcescens, which thrives in moist environments like toilets and showers.

No, Serratia marcescens is not known to be a waterborne disease and poses minimal health risks to healthy individuals. It can, however, cause opportunistic infections in immunocompromised individuals, so careful hygiene is important.

Some filters, particularly activated carbon filters, remove chlorine from the water supply. Chlorine normally inhibits bacterial growth. Without this disinfectant, airborne Serratia marcescens can more easily colonize and thrive in standing water.

Add a quarter-cup of chlorine bleach to the toilet tank, let it stand for 15-20 minutes, then flush it a couple of times. Do not leave bleach in the tank for prolonged periods, as it can damage rubber seals and valves.

A vinegar and water solution can help clean the area and remove mineral deposits and soap scum that the bacteria feed on. However, a chlorine-based product is more effective for true disinfection and killing the bacteria itself.

A whole-house water filter does not typically resolve the pink slime issue because Serratia marcescens is an airborne issue that settles on surfaces, not a contaminant carried in your home's water supply.

Once established, the organism is difficult to eliminate entirely, so periodic and thorough cleaning is the best approach. Regular cleaning and drying of moist surfaces should be part of a routine maintenance schedule.