Have you ever noticed a film of slime on your cat’s water bowl? While it may gross you out, there’s actually nothing to worry about – in most cases, it’s just harmless algae.

Algae is a type of plant that can grow in water and it’s very common in fish tanks. It grows best in warm, humid environments, and it’s usually not a problem in most water bowls. However, if your cat likes to play with her water or if she drinks from the bowl frequently, that might be enough to start the growth process.

Here’s a closer look at why cat water bowls get slimy and how you can keep your kitty’s drinking station clean.

The Science Behind the Slime

That slimy stuff in your cat’s water bowl is most likely algae. Algae are primitive plant-like organisms that can grow in both fresh and salt water. In fact, they’re the oldest known plants on Earth, and they come in many different shapes and sizes.

Why Do Cat Water Bowls Get Slimy?

While some types of algae are beneficial (like the kind used to make spirulina supplements), the type that grows in cat water bowls is harmless.

Algae need four things to survive and thrive: sunlight, water, carbon dioxide, and nutrients. If even one of these elements is missing, growth will be stunted. For example, algae won’t grow in a dark room or if the bowl is dry.

In most homes, though, there’s plenty of light and humidity for algae to flourish – which explains why it shows up so often in cat water bowls.

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The good news is that there are a few things you can do to prevent the slime from forming in the first place:

  • Change the water regularly – Bacteria need time to grow, so the more frequently you change your cat’s water, the less chance there is for bacteria to form. Try to clean out the bowl and refill it at least once a day.
  • Use filtered water – Running tap water usually has traces of chlorine, which can help kill bacteria. However, some cats don’t like the taste of chlorine and will avoid drinking water that contains it. In this case, using filtered or distilled water may be a better option.
  • Wash the bowl regularly – Even if you’re changing the water every day, it’s important to wash the bowl itself on a regular basis. Bacteria can cling to the sides of the bowl and continue to grow even when fresh water is added. Aim to wash your cat’s bowl with soap and hot water at least once a week.

Keeping Things Clean

While there’s no need to panic if you see a bit of slime in your cat’s bowl, it is important to keep things clean for sanitation purposes. The best way to clean a slimy cat bowl is to remove it from the environment (i.e., take it outside) and scrub it with hot, soapy water.

You can also use a 1:1 ratio of white vinegar and water to break down the slime. Just be sure to rinse the bowl thoroughly afterward so your cat doesn’t end up taking a sip of vinegar.

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If you notice that the bowl is getting slimy more often than usual, it might be time to check the quality of your home’s tap water. Minerals in hard water can promote algae growth, so using filtered or distilled water may help keep things under control.

You can also try adding a splash of lemon juice or hydrogen peroxide to the bowl; both of these agents have algaecidal properties that can help nip the problem in the bud.


A slimy film on your cat’s water bowl may not be pretty, but in most cases, it’s nothing to worry about – it’s just harmless algae.

Just like humans, algae need four key factors to survive: sunlight, water, carbon dioxide, and nutrients. Without even one of these factors, their growth will be stunted or stopped altogether.

Luckily, there are some simple strategies you can use to prevent algae from forming in your cat’s water bowl. You should try to change the water regularly, use filtered water, and wash the bowl regularly. If you notice that the slime seems to be forming more often than usual, it may be a sign of hard water or another issue with your tap water.

You can try using filtered or distilled water instead, adding a splash of lemon juice or hydrogen peroxide, or consulting a water quality expert for help managing the problem.

In any case, keeping things clean is key to ensuring that your cat always has access to fresh and safe drinking water.

About the author

I started working as a quality control manager with the Water Authority of Nassau County in 2005. After a few years, I moved into Water Waste Prevention, where I currently work as the production supervisor. I love my job and the people I work with, but most of all I love spending time with my family.