Are Coffee Grounds Bad for Septic Systems? (Key Tips)

I must admit when cleaning out the French press I have accidentally washed some coffee grounds down the sink a few times.

Luckily it hasn’t got stuck down the drain and we don’t have a septic tank, but if we did have a septic system would this block it?

Coffee grounds are very bad for your septic system as they clump together to block it and can’t be easily removed. They also change the pH level in the septic tank so the bacteria that break down waste will not work properly, meaning your septic system could stop working completely.

Let’s dive down into the subject of coffee grounds and septic systems in more detail, and discover why it’s a bad idea to let them get in there (and how you can stop them from getting down there in the first place)…

Are Coffee Grounds Bad for Septic Systems?

Why is It a Bad Idea to Put Coffee Grounds in My Septic Tank?

Coffee grounds really shouldn’t enter your septic tank because they could block it. They may look like they’ll simply innocently dissolve in liquid, but unfortunately, they stay stubbornly solid.

Unlike instant coffee, grounds aren’t designed to dissolve in water. Coffee grounds aren’t powdered and so they won’t simply melt away. They’re actually tiny fragments of crushed bean, so although they’re really really small, they’re actually solids.

Used coffee grounds also have an unfortunate tendency to clump back together, forming a solid mass. This clump of used coffee can actually clog up your drainage system, so must never be allowed near your septic tank.

As well as this, the slightly acidic grounds can alter the pH of your tank, and we’ll look at that in more detail in a moment.

How Long Does It Take Coffee Grounds to Decompose in a Septic Tank?

The bad news here is that they might not break down at all. If you keep flushing more grounds into the system, the coffee clumps will grow and could end up causing serious problems.

Coffee is very slow to break down full stop, and it will even take at least three months to break down in soil. While this makes it an excellent slow-release fertilizer, it also makes it firmly “unflushable”.

Will Coffee Grounds in My Septic Tank Affect the PH Level?

Yes, coffee grounds will affect the pH level in your septic tank. There’s actually a pretty delicate ecosystem going on inside that slurry inside the tank, which uses bacteria to break down the waste.

These helpful bacteria thrive in a pH neutral environment. When they’re happy with the chemical balance, they simply get on with doing their essential job. Now raise the acid level by adding coffee grounds, and the bacteria become less effective. 

The whole septic system relies on effective waste breakdown to work. So not only will coffee grounds cause blockages in the system, they can also stop it from functioning properly as a waste management system as well.

If you want to know more about how a septic system works, this is a clear explanation.

How Can I Stop Coffee Grounds Getting Into My Septic Tank?

We looked at several ways to keep coffee out of your drainage system in our earlier article.

The key is to treat them as solid waste and not as something that can be rinsed or flushed away. The exact same principle applies to septic systems as to other household drainage systems.

So, tip out used grounds into the garbage or compost before washing the pot or filters. It’s a good idea also to wipe these out before you wash them, with an aim to keep as many grounds out of the sink as possible.

To be extra sure that nothing is going down the sink that shouldn’t, you can buy a mesh filter for your plug hole. Choose a very fine mesh, and it should catch the majority of the remaining grounds.

Disposable filters are good, because you can recycle those immediately without having to wash them.

If any grounds are really stuck to the side of say, the French press, swill water around inside the pot then pour it straight onto the garden. The plants will love it, and there’s no risk of grounds going down the drain.

Will Paper Coffee Filters Break Down in My Septic Tank?

Most paper coffee filters sold these days are 100% biodegradable, and that’s great news. Thing is, while the papers will rot down, the grounds inside them won’t. So even though the disposable filter itself is no threat, its contents remain a problem.

However, the fact that paper filters break down does make the used coffee grounds easier to dispose of.

When it’s cool, you can simply pick up the whole soggy clump of filter and grounds, and chuck it on the compost. That’s a simple, easy, and eco-friendly way to get shot of your used coffee grounds.

How a Septic System Works (It Can't Handle Your Coffee Grounds)
How a Septic System Works (It Can’t Handle Your Coffee Grounds) 🙂

What Else Can I Do With My Coffee Grounds?

We mentioned compost just now: are there other uses for used coffee grounds? There certainly are, and we’ll go through them here.

  • Compost. Finished brewing your coffee? You can empty your coffee grounds straight into the compost pile or bin, where the worms will absolutely love them
  • Fertilizer. You can also scatter coffee grounds directly onto the soil as a fertilizer, as they’re a natural source of nitrogen.Sprinkle them at the base of plants or across your lawn, where they will slowly release their nutrients
  • Cleaning scrub. Make the most of the grounds’ abrasive texture by using them as a scrub. They’re perfect for scouring pans, and help get rid of stubborn, baked-on debris
  • Beauty scrub. Caffeine is great for your skin, and you can mix grounds with other natural ingredients to make a facial, body, or even a hair scrub. Here’s a simple recipe for a natural facial scrub made with used coffee grounds (video below too).
  • Bug repellent. Insects like mosquitoes really don’t like the smell of coffee. You can scatter grounds around to keep them away, or even better, burn them. You can use old coffee grounds to make scented candles: lovely for humans, less pleasant for bugs
  • Deodorizer. You can use a dish of coffee grounds in much the same way as you use bicarbonate of soda: to absorb unpleasant odors. Place the dish in the refrigerator or microwave (when not in operation) to soak up lingering smells
  • Get crafty. Yes, you can even use coffee grounds as a natural dye or paint. Time to get creative with that old coffee!

As you can see, if you flush away coffee grounds, you’re actually wasting a precious, free resource. There are so many good ways to use up those old grounds, that there shouldn’t be any need for them to be anywhere near your septic system or drains.