The short answer
No. Coffee grounds shouldn't go down the sink.
They don't dissolve. They sink, settle in the bends of your pipes and clump together with grease and soap. One morning's worth won't block a drain, but months of rinsing out the cafetière will.
Put them in your food waste caddy, your compost or your garden instead. We roast coffee at Old Spike Roastery in London and run cafés across the city, so we get through a lot of grounds. None of them go down the sink.
Why do coffee grounds block drains?
Coffee grounds block drains because they're heavy, they don't break down in water, and they stick to grease.
Ground coffee is tiny particles of roasted plant fibre. Brewing pulls out the flavour, but the fibre stays. Rinse it away and it doesn't wash through like liquid. It drops out wherever the water slows down: the U-bend under your sink, joints, long flat runs of pipe.
On its own, that's a slow build. The problem is what it meets down there. Kitchen pipes carry cooking fat, oil and soap scum, which coat the inside of the pipe. Grounds stick to that coating and bulk it out. Yorkshire Water describes the result as a sticky sludge (Yorkshire Water).
Scale that up and you get to London's sewers. Thames Water clears thousands of fat-related blockages a year, and its advice is simple: bin food waste and fat, don't sink it (City AM). Grounds aren't the main ingredient in a fatberg, but they help hold one together.
There's an online myth that coffee grounds clean or deodorise your drains. They don't. They're part of the problem, not the fix.
What if I have a waste disposal unit?
A waste disposal unit doesn't help. Grounds are already finer than anything it can grind.
A disposal unit chops food into smaller pieces. Coffee grounds are already small, so there's nothing for it to do. They pass straight through and settle in the pipe beyond it. Worse, wet grounds tend to clump together rather than break down, so they can pack around the blades and slow the unit itself (Mr. Rooter).
The same goes for the outside drain. Never tip coffee, or grounds, into a street drain or garden gully. In much of the UK those carry rainwater straight to rivers, not to a treatment works. In 2025 a London commuter was fined £150 for pouring her coffee into one (Gigazine, summarising The Conversation).
What should you do with used coffee grounds?
Put them in your food waste caddy or your compost. If you have a garden, use some there.
Food waste caddy. This is the easiest answer for most people. Since 31 March 2026, councils in England have had to collect food waste from every household weekly, free of charge, including flats (GOV.UK). Some councils have transitional arrangements, so check yours. Food waste is turned into compost or biogas rather than going to landfill. Paper filters usually go in with the grounds, but check your council's list.
Home compost. Grounds are a good compost ingredient. They count as "greens", the nitrogen-rich layer, so balance them with "browns" like cardboard, dry leaves and paper.
In the garden. You can scatter a thin layer around plants or dig them lightly into soil. Keep it thin. A thick layer can dry into a crust that sheds water instead of letting it through.
At the sink. Knock the cafetière out into the caddy before you rinse it. A fine mesh sink strainer catches whatever's left. Wipe the last bits from the AeroPress or portafilter with a used paper towel and bin that too.
If you use pods, they're a separate question. Most aluminium and plastic pods don't go in food waste. Check the manufacturer's recycling scheme.
Already poured grounds down the sink? Here's how to clear it
Start with a plunger. If that doesn't work, clean out the U-bend. Call a plumber if neither does.
The usual signs are water draining slowly, a gurgle from the plughole or a musty smell. Work through these in order:
- Plunge it. Leave a few centimetres of water in the sink to make a seal. Cover the overflow hole with a damp cloth, then plunge firmly for 20 to 30 seconds.
- Clean the U-bend. Put a bucket underneath and unscrew the trap by hand. Most kitchen traps are plastic and come apart without tools. Scoop out the sludge, rinse the trap in another sink or outside, and screw it back hand-tight.
- Flush with hot water. Run the hot tap for a minute or two with a squirt of washing-up liquid to shift loosened grease. Avoid pouring boiling water into plastic pipes.
- Try a drain snake. If the blockage is further down, a cheap plastic drain snake from a hardware shop can reach past the trap.
- Call a plumber. If water still won't clear, or it backs up in more than one plughole, the blockage may be in the shared drain. Contact a plumber or your water company.
Go easy on chemical drain cleaners. They're harsh on pipes and skin, and dangerous if they splash back when you plunge.
FAQ
Can a small amount of coffee grounds go down the sink?
A few stray grounds won't cause a blockage on their own. The problem is the habit. Small amounts every day build up in the U-bend and stick to grease.
Do coffee grounds dissolve in water?
No. Brewing extracts the flavour, but the solid plant fibre is left behind. It doesn't break down in your pipes.
Can coffee grounds go down a waste disposal unit?
No. Grounds are already too fine for the unit to grind. They pass through and settle in the pipe beyond it, and they can clump around the blades.
Do coffee grounds clean drains?
No. That's a myth. Grounds add to blockages rather than clearing them.
Can coffee grounds go in the food waste bin?
Yes. Since March 2026, councils in England must collect food waste weekly from all households. Grounds and paper filters usually go in. Check your council's list.
Can I pour leftover coffee down the sink?
Liquid coffee down a kitchen sink is fine in small amounts, as it goes to a treatment works. Never pour it into a street drain, which can lead straight to a river.
The bottom line
Coffee grounds don't dissolve, they stick to grease, and they build up where you can't see them. Knock them into the caddy, rinse the cafetière after, and your pipes will thank you.
If you're brewing at home every day, brew something worth the effort. We roast specialty coffee in London for cafés, offices and home brewers. We're profit-for-purpose, so every bag also funds paid training and jobs for people experiencing homelessness. Coffee that works harder.
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