Stop Pouring Coffee Grounds Down the Drain—Here’s Why It’s a Big Mistake

Washing your morning coffee grounds down the drain after enjoying your cup is convenient and minimizes mess, but it's not as harmless as you might think. Tossing coffee grounds into the sink can cause serious plumbing problems over time. To learn more about this coffee clean-up habit, we spoke to an expert about why coffee grounds are a common cause of slow drains and costly clogs, and what you should do with your used grounds instead.

What Happens When Coffee Grounds Go Down the Drain

After you've brewed your morning coffee, you might be tempted to toss the grounds into the sink and rinse them away with water. While that habit may seem harmless, it can lead to significant plumbing issues over time.

The problem is that coffee grounds don't dissolve in water—they can clump together and build up in your pipes, leading to blockages. Unlike other food items that don't clump the same way, coffee grounds tend to accumulate at the low points or bends of a drain system, such as P-traps, says Ryan Meagher, from BVM Contracting.

"Coffee grounds are generally more dense than water, so they will sink into these low points and stay there," says Meagher. "When things are allowed to accumulate and stay in place in drain lines, it leads to less flow and potentially clogged pipes."

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How Coffee Grounds Make Clogs Worse

When you toss the coffee grounds into the sink, they mix with grease, soap scum, and food residue that cling to the pipe walls. Together, they form a thick sludge that builds up over time, slowing the drains and causing unpleasant odors—and potentially costly plumbing repairs to clear the drain if the habit continues.

To prevent food and coffee ground blockages, Meagher recommends installing P-traps with a built-in drainage point at the lowest point. This will allow for easier maintenance and help prevent these types of clogs from happening.

The Right Way to Dispose of Coffee Grounds

Instead of rinsing your coffee grounds down the sink, consider putting them in your municipal food waste bin, if you have one. You can also use them in compost or as lawn or garden fertilizer, says Meagher. In fact, there are myriad ways to use coffee grounds around the house and in the garden. Lastly, you can simply throw them in the trash.