The Rush to Flush: What Impact Does Your Cat's Waste Have on the Water System?

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impact of cat waste on the water system

I know it sounds weird, but I often think about which inventions have been the most revolutionary: the lightbulb, the air conditioner, the refrigerator, vaccines... But there’s one invention I am always astounded by: the toilet. Well, the entire plumbing system, really. How amazing is it that we push a handle and our waste magically disappears from our homes and minds. And thinking about toilets made me wonder: where does kitty waste and flushable litter go after we push the handle and how does it affect our environment?

If you’re a green cat parent like me, you’ve probably wondered the same. So, I’ve decided to focus on the journey of flushable cat litter from the commode and beyond for this article. And trust me, this topic is not a waste of your time.

What Happens After You Flush Cat Litter: Understanding Your Wastewater System

What Happens After You Flush Cat Litter

Do you remember your sixth-grade teacher talking about the Roman aqueducts like they were the most incredible invention in human history? Well, they kind of are. The aqueducts were the great-great-great-grandmother of our sewer system. I wonder if they considered flushable litter?

The sewer system makes our cities more sanitary and wastewater treatment facilities pull harmful impurities from the wastewater, making it possible to reintroduce ‘used’ water into the environment, and the way they work is just incredible.

Let’s take a closer look.

Waster water treatment plant in industry for environment protection by aeration pump

Most cities rely on sewer systems. Some people in more remote areas rely on septic tanks (which I will get into later). But both systems use gravity to move water and waste through pipes to treatment plants. Most cities build their wastewater facilities at the lowest elevation in town since gravity naturally carries water to the lowest point possible. When a city’s low-lying elevation point isn’t the best for cleaning wastewater or the landscape isn’t conducive to relying on gravity, cities install pumps and lifts that push water up and over hills.

After the water goes on a wild ride from the toilet to the wastewater treatment plant, the wastewater begins its transformation from waste to environmentally safe water.

Imagine you flush your kitty’s litter and waste. There’s about 3 gallons of water, the litter, and waste. When this mixture makes it to the wastewater facility, the solids (the litter and poop) get separated out using a strainer and several screens. In fact, half of the solids and bacteria become trapped during this process.

What about the other half of the solids and

bacteria? The water then gets either chlorinated, killing bacteria or they add some other hungry bacteria to the mixture. The hungry bacteria gobble up the harmful bacteria and become heavier than the liquid, eventually setting on the bottom. This makes it easy to remove the remaining bacteria, poop, and other solids. This part of the process pulls 90% of the remaining bacteria out of the water.

What about the rest of the bacteria and pollutants?

Then the remaining water gets filtered. Most treatment facilities also add chemicals to neutralize phosphorus and nitrogen. They also remove heavy metals and other pollutants to make the water more environmentally-friendly.

Now the one ooey-smelly water ready for its second life. Treated wastewater finds new life by re-entering the water system through rivers, lakes, the Intracoastal, and release points near the ocean. This is why it matters what we flush.

Not all that we flush is equal. Wastewater systems are not designed to handle excessive chemicals and some waste. And some older pipes (cough, cough: New York City) can’t easily handle clumping solids like flushable cat kitty litter in addition to the millions of flushes they see daily. Grease and fats are the worst culprits when it comes to clogging pipes.

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The right choice, for your kitty and the earth.

As for Your Septic System

I said I’d get to this one, didn’t I? The same filtering process takes place on a smaller scale but beneath your yard when you have a septic tank. The main difference is a septic system doesn’t have the same chemicals in the purification system.

In a septic system, the solids, like cat poop, get split off while the water seeps back into the ground, eventually mixing with groundwater. Most people call this process “percolating,” but I don’t like comparing wastewater integrating into the ground to my morning coffee.

This means the same general flushing rules apply to septic systems, but keep in mind that if there’s a clog in your underground pipes, the poopy water will bubble up into your yard, and you’re financially responsible for fixing the problem. Yuck!

How Does Cat Waste Affect the Wastewater System and Environment?

Ok, now that you understand the wet-and-wild ride waste takes from the time you push the flush lever to when it’s reintroduced into the water system, we can take a closer look at how your cat’s poop and urine affect the ecosystem and environment.

How Does Cat Waste Affect the Wastewater System and Environment?

For the most part, water treatment and reintroduction have a positive effect on the environment and our lives. This water refills aquifers to prevent saltwater intrusion. It can also be used to water crops (like tofu) to reduce the need to use water from natural areas and disrupting the natural habit for many species. And it’s nice to think that the water we flush doesn’t end up stored somewhere never to see the light of day again.

Crops love nitrogen and phosphorus in moderation, which makes waste water perfect sense these are common byproducts of waste.

Overall, treated water has to be very, very clean to meet the standards to be released. But this water still can contain pollutants like viruses and bacteria that manage to squeak through.

One of these pollutants we have to be mindful of is cat waste. Cat waste is listed as a pollutant by the EPA. Why? When it comes to your cat’s waste, the factors that are not Earth-friendly include toxoplasmosis, parasites, viruses, medications, and ammonia.

Cat Poop and Your Wastewater

Your cat’s poop must go somewhere. Your options are to scoop that poop and bag it, compost it, or flush it.

options to dispose of your cat litter: trash it, compost it, or flush it.

Scooping and bagging tend to create the most waste and have the largest negative impact on the environment if you factor in the plastic and longevity of clay litter at the landfill. With 90 million cats in the U.S. this results in 2 million tons of cat litter in landfills each year.

Composting your cat’s poop and biodegradable litter is often considered the most eco-friendly poo practice since the waste is in one spot and will decompose, turning into usable soil. Although, it’s important to keep in mind that rainfall eventually carries the poo particles and pollutants into the water system.

So, what about flushing that feline poo?

Toxoplasmosis and Other Parasites

Are you one to rush to flush that used cat litter and should you change this habit to be a better eco-friendly cat momma?

The most threatening parasite cat feces can contain is toxoplasmosis. And while I would love to dive into the details of this strange parasite ( like: did you know it can reproduce asexually?), I will refrain. This parasite can cause infected people to feel like they have the flu. It can also harm gestating babies if a mother contracts it, and it can do damage to marine mammals when it remains in wastewater that’s reintroduced to waterways. And the problem continues to get worse. Climate change has made toxoplasmosis spread more easily.

Luckily, most indoor cats that don’t eat raw meat aren’t at risk for carrying toxoplasmosis. And if they do, they spread the bacteria only while they are infected, which is about 1 to 3 weeks.

While a wide range of animals can be affected by toxoplasmosis, its effect on Pacific marine mammals is the most heartbreaking. Because of the expansive coastal populations in California, a lot of wastewater winds up in the ocean, profoundly impacting marine mammal populations.

Wastewater that washes out to sea will eventually sink to the sea floor where crabs and other sea life will swallow it and become carriers.

Then marine mammals become infected by eating these crabs, starfish, and tiny fish that carry the parasite. Toxoplasmosis has been reported in dolphins, humpback whales, sea otters, and monk seals. The already meager sea otter population has been reduced by 84% from 25,000 to 2,500. And there’s no way to count how many marine mammal miscarriages resulted from toxoplasmosis.

the risks of flushing cat litter if they have toxoplasmosis

This is to say, our wastewater facilities are great but not perfect. It’s hard to imagine what the impact on the Earth would be if we didn’t have waste treatment. Toxoplasmosis and some other parasites and bacteria often slip through the process and harm these intelligent and majestic creatures.

Kitty Urine: Ammonia and Medications

While toxoplasmosis if the best-known culprit when it comes to flushing your kitty’s litter, her urine also contains some eco-contaminates. Remember the reason your cat’s box gets stinky? That same ammonia also impacts our environment. In places like Pennsylvania, people report smelling cat urine near wastewater facilities. This is likely from small amounts of cat urine getting flushed in a rush.

Ammonia from cat urine can also negatively affect

  • Aquatic creatures
  • Vegetation growth
  • Soil by becoming too acidic
  • Bodies of water by becoming overly acidic


unused, flushed cat prescription medications can have a negative effect on the planet

Just as the wastewater facility can’t pull all bacteria out of treated water, they also can remove 100% pharmaceutical pollutants. Most flushed prescriptions come from cat parents flushing unused pills, but some pass through your cat’s urinary system. While medicine is helpful for your sick kitty, it’s less-than-helpful for our planet.

What Can You Do to Minimize Your Impact on the Environment?

In the words of a great philosopher, Kermit the Frog, “It’s not easy being green.” Well, it’s not always the easiest option, but it is the right option. So, how can you do your part as an eco-friendly cat parent? We have some tips to keep in mind:

  • If your cat has been outside or consumed raw meat, bag her poop for about three weeks afterward and send it to the landfill rather than down the toilet. This reduces the risk of introducing toxoplasmosis into waterways. Remember, toxoplasmosis stays active for up to 18 days.
  • Compost your kitty’s waste with heat treatment to kill as much bacteria as possible, especially if you’re one of our West Coast kitty parents. 140-degrees Fahrenheit kills most bacteria and viruses. Commercial compost facility heat their waste beyond this. If you’re unsure if your compost got hot enough, do not use the compost on your fruits or veggies.
  • Use environmentally friendly, biodegradable, and renewable cat litter. These products take advantage of reusing wastewater while benefiting the planet by not mining our clay resources.
  • Keep your kitty indoors, so she’s less likely to be exposed to toxoplasmosis.
  • Dispose of your cat’s medications properly. Ask your vet if they have a program to take back unused prescriptions.
  • Use biodegradable, eco-friendly cat waste bags if you’re bagging your kitty’s waste.
how can I be a more eco-friendly cat owner

Should You Rush to Flush?

The final answer to this question is that it’s up to you. Opting to commercially compost your kitty’s waste or heating your home compost to 140-degrees to kill most bacteria and use it to fertilize your flowers is the most green option you can choose.

If you’re one curious cat (like me), I suggest you contact you city’s wastewater treatment program, go on a tour of the facility and ask as many questions as you can. They can tell you where your specific wastewater ends up and what pollutants tend to sneak through their system.

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Introducing TofuKitty litter

Hi, I’m Molly, an environmental ecologist and creator of TofuKitty. I created a new kind of litter that was made with you, your kitty, and the planet in mind. You shouldn’t have to choose between effective cat litter and making green choices. My litter is:


Triple odor protection


Dust free




Low tracking

Chemical free

Super absorbent

Pest free

Soft on paws

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The right choice, for your kitty and the earth.
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