Your slimy cat water fountain has biofilm

The slime in your fountain is biofilm, a community of microorganisms attached to a surface and enclosed in a matrix of material they produce.¹ Growth occurs where moisture, nutrients, and a surface come together.² Pouring out the water removes the liquid, but removing the biofilm requires cleaning the surface itself.

Is it normal for a cat water fountain to get slimy?

Yes, biofilm is normal in most water systems.³ The slime you feel is the sticky substance bacteria release to anchor themselves to moist surfaces.⁴

Food and soap residue alongside pink slime

The pink color is often caused by Serratia marcescens.⁵ This bacterium grows in moist places where phosphorus-containing materials or fatty substances collect. Soap and food residue in pet water dishes are listed among the sources of these substances.⁶ A pink patch can reappear after you wash the bowl because the bacterium spreads through the air and grows well in damp places.

Biofilm is attached to surfaces

Biofilm can form in water that is standing still or flowing.³ We did not find a published study that sampled the internal components of cat water fountains, so this explanation applies general biofilm research to the fountain you use. In a recirculating fountain, circulation means that the same water is pumped around for reuse.

When you pour water into the sink, you change the liquid in the fountain. You have not scrubbed the surfaces that held it. A gentle rinse does not remove biofilm from the surface.¹

Two tanks for filling and emptying

In the HAPAW Smart Cat Water Fountain, water remaining in the bowl after your cat drinks goes into the tank you empty. You pour that water away.

The pump draws only from the tank you fill. All surfaces exposed to water need scrubbing, including the side you fill, just as on any fountain.

What should you take apart and scrub to remove biofilm?

Use soapy water on washable surfaces and scrub with a sponge or brush.⁷ After scrubbing, rinse away the soapy water and dirt that remain.

Take apart and thoroughly clean the removable parts specified in your fountain’s manual; replace any filter according to the manufacturer’s instructions.⁸ Washable surfaces on your own fountain that water reaches but that are hidden during ordinary use, such as a covered seam, should be scrubbed with a brush.

Sources

1. Rodney M. Donlan, 2002. Biofilms: Microbial Life on Surfaces. CDC, Emerging Infectious Diseases.
2. Montana State University, Center for Biofilm Engineering, undated. Biofilm basics: Section 2 — Where do biofilms grow?
3. CDC, 2003 guideline; webpage dated January 11, 2024. Appendix C. Water.
4. Montana State University, Center for Biofilm Engineering, undated. Biofilm basics: Section 1 — What are biofilms?
5. Portland Water District, undated. There is pink slime in my shower. What is it and is it harmful?
6. Gwinnett County Department of Water Resources, undated. Facts About Serratia marcescens.
7. CDC, February 18, 2026. About Cleaning and Disinfecting Pet Supplies.
8. International Cat Care, 2024. Encouraging your cat to drink, p. 5.