Cat Water Fountain Filter Guide: When and How to Change It

By the PETME2 Team · Updated October 2026 · General information, not veterinary advice

What does a cat water fountain filter do?

A fountain recirculates the same water over and over. The filter sits in the water path and catches things you do not want floating around, such as cat hair, dust, and small bits of food. Many filters also contain activated carbon, which is commonly used to reduce odors and improve how water tastes, and ion-exchange resin, which is often included to reduce some minerals from tap water.

Different fountains use different filter styles. Here are the most common:

Foam or sponge pre-filters

These wrap around or sit in front of the pump. Their main job is to catch hair before it reaches the pump. They are usually rinsed often and replaced less often.

Cartridge filters

A cartridge is a small pouch or frame filled with carbon and resin beads, often wrapped in mesh. The PETME2 Transparent 2.2L fountain uses a filter cartridge.

Multi-layer filters

These stack several materials together, such as a fine mesh, a cotton or foam layer, activated carbon, and resin. Both the PETME2 3.2L stainless steel fountain and the 2.2L fountain with stainless steel tray use a 4-layer filter.

Filter layers compared

If your filter has several layers, each one has a different job. This is how the most common layers are typically used:

Do you really need a filter in a cat water fountain?

Not strictly, but it is well worth using one: a filter protects the pump from hair and helps keep the water cleaner between washes.

This is one of the most common questions cat owners ask. Most fountains will still pump water without a filter, but the filter does two useful jobs:

• It protects the pump. Hair is the number one reason pumps get noisy or slow down. The filter catches much of it first.
• It helps keep water cleaner between washes. Hair, dust and food bits get trapped instead of circulating.

Without a filter, you will need to clean the bowl and pump more often. If the cost of filters is the worry, rinsing your filter every week helps it last through its full replacement window. And remember: a filter helps between cleans, but it never replaces the weekly clean.

How often should you change a cat fountain filter?

Change it about every 2 to 4 weeks, and lean toward every 2 to 3 weeks if you have several pets, a long-haired cat or very hard tap water.

The 2 to 4 week range is a general guide. Where you land in that range depends on your home:

Always check your fountain's manual. If it gives a different schedule, follow the manual.

How do you know when to change the filter?

Replace the filter when it changes color, slows the water flow, smells musty, or makes the pump louder, even if the date has not come yet.

• Color change. A white or light filter that has turned gray, brown, or green is done.
• Slower flow. A clogged filter can reduce how much water reaches the spout.
• Louder pump. When water struggles to get through, the pump can work harder and sound noisier.
• Smell. A musty or sour smell means it is time to replace the filter and clean the fountain.
• Visible slime or hair stuck in the filter that will not rinse out.

How do you change a cat fountain filter?

Unplug the fountain, remove the old filter, clean the fountain while it is apart, prepare the new filter as the package says, fit it snugly the right way, then refill and plug in.

1. Unplug the fountain.
2. Remove the cover and lift out the old filter.
3. Clean the fountain while it is apart. This is the perfect time for the weekly clean (see our guide to cleaning a cat water fountain).
4. Prepare the new filter. Many carbon filters should be rinsed or soaked in clean water for a few minutes before use. This removes loose carbon dust and helps them sit properly. Follow the instructions on the package.
5. Put the new filter in place. Make sure it faces the right way and fits snugly so water goes through it, not around it.
6. Refill and plug in. Check that water flows normally. A few small bubbles at first are normal.

Which way does the filter go in a cat fountain?

Getting the direction right matters, because water should pass through the filter, not around it. Here is how to check:

• Look for markings. Many filters have an arrow, a "top" label, or a small tab that shows which way they face.
• Match the shape to the slot. Filters are usually shaped so they only sit snugly one way.
• Check for gaps. If you can see a gap around the edges, water will flow around the filter instead of through it. Reseat it.
• Soak it first if it floats. Carbon filters often float until they are soaked through.

If you are not sure, the diagram in your fountain manual is the best guide.

Can you reuse or wash a filter?

You can (and should) rinse a filter with clean water during weekly cleaning. Do not use soap, because it can stay in the filter material and affect the water. But rinsing does not "recharge" carbon or resin. Once those materials are used up, they stop working well, even if the filter looks okay. That is why filters have a replacement window.

Foam pre-filters are a bit different. Many can be rinsed and reused for longer. Check your manual to see which parts are reusable.

How do you clean a cat fountain filter?

Rinse it under clean running water with no soap, and gently pick off any hair.

A quick rinse each week keeps the filter working well until its change date. It takes about a minute:

1. Take the filter out during your weekly fountain clean.
2. Hold it under cool or lukewarm running tap water.
3. Gently pick off any hair caught on the mesh. For foam layers, squeeze gently a few times.
4. Do not scrub carbon pouches hard or open them.
5. Skip soap, bleach and vinegar on the filter itself.
6. Put it back facing the right way and switch the fountain on.

Tips to make filters last longer

• Rinse weekly. Removing hair early keeps the filter working through its full cycle.
• Brush your cat, especially during shedding season.
• Keep the fountain away from food and litter so less debris gets in.
• Use filtered water if your tap water is very hard.
• Write the change date on a piece of tape on the fountain base, or set a phone reminder.
• Buy filters ahead. Keeping a spare at home means you never stretch an old filter too long.

Buying replacement filters

A few simple habits make filter changes painless:

• Match your exact model. Many stores sell "universal" filters, but fit matters. A loose filter lets water flow around it.
• Buy a few at a time. Keeping a spare at home means you never stretch an old filter.
• Think in cost per month. If you change filters every 3 to 4 weeks, you will use about one per month.
• Check before you buy a fountain. Make sure replacement filters for that model are easy to find.

Common filter mistakes

Does a fountain with a better filter make a difference?

A good filter makes upkeep easier, but the bigger factors are how often you clean and how easy the fountain is to take apart. When choosing a fountain, look at the filter type, the cost and availability of replacements, and whether the pump is easy to reach. You can see the filter type for each model in our cat water fountain collection. All PETME2 orders ship free in the U.S. with a 30-day money-back guarantee.

Frequently asked questions

How often should I change my cat water fountain filter?

Most cat water fountain filters should be changed about every 2 to 4 weeks. Change it sooner with several pets, a long-haired cat or very hard tap water. If your fountain's manual gives a different schedule, follow the manual.

What does a cat water fountain filter do?

A cat water fountain filter catches hair, dust and food bits as the water circulates, which helps protect the pump. Many filters also contain activated carbon, commonly used to reduce odors and improve taste, and ion-exchange resin, often included to reduce some minerals from tap water.

What happens if I don't change my cat fountain filter?

An old filter can clog, slow the water flow, make the pump work harder, and stop catching hair and debris well. The water can also start to smell. Changing it on schedule keeps the fountain working as it should.

Can I run a cat fountain without a filter?

Most fountains will still pump water without a filter, but hair and debris will reach the pump more easily. You will also need to clean the bowl and pump more often. It is best to use the filter the fountain was designed for.

Can you reuse a cat fountain filter?

You can rinse and reuse a filter until its replacement date, but rinsing does not recharge the carbon or resin inside. Once those materials are used up, they stop working well, even if the filter looks fine. Many foam pre-filters can be rinsed and reused for longer, so check your manual.

How do I clean a cat fountain filter?

Rinse it under cool or lukewarm running water during your weekly clean. Gently remove any hair and squeeze foam layers. Do not use soap, and do not open or scrub carbon pouches.

Can I wash a cat fountain filter with soap?

No. Soap can stay in the filter material and affect the taste and smell of the water, which may put your cat off drinking. Rinse fountain filters with plain clean water only.

Why is my new filter making the water cloudy?

New carbon filters can release a little fine carbon dust. Rinsing or soaking the filter before use, as the package directs, usually prevents this. If the water is already cloudy, empty it, rinse the filter again and refill.

Do I need to soak a new fountain filter?

Many carbon filter packages recommend a rinse or a short soak before use. This removes loose carbon dust and helps the filter sink into place. Follow the directions on your filter package.

Which way does the filter go in a cat fountain?

Look for an arrow, a "top" label or a tab, and match the filter to the shape of its slot. It should sit snugly with no gaps so water passes through it, not around it. Your manual will have a diagram if you are unsure.

How do I know if my filter is installed wrong?

Signs include water flowing around the filter instead of through it, a filter that floats, weaker flow, or a noisier pump right after a change. Take it out, check the direction, and reseat it firmly.

Are all cat fountain filters the same?

No. Filters are usually made to fit specific fountain models. Always use a filter that matches your fountain's size and shape so water passes through it properly.

Why is my cat water fountain not working after a filter change?

The most common causes are a filter that is not seated properly, air trapped in the pump, or a water level below the min line. Reseat the filter so it sits snugly, top up the water, and let the fountain run for a few minutes so bubbles clear. If it still does not flow, check that the pump impeller spins freely.