Coffee grounds and water systems
September 11, 2007 5:50 PM   Subscribe

A coffee related, although mildly different, question that doesn't involve waste disposal units like the ones in the search seem to...

I have been washing my coffee grounds down the sink. They are, in my mind, biodegradable and pretty small after they have gone through the filter thing in the sink. They aren't, I'd say, going to clog anything.

Now I know there are many many opinions about the 'not washing it down the sink/disposal unit' and all that, but they seem to revolve around 'the rubbish (I believe some call it 'trash' or 'garbage', bless their colonial hearts) is a better place for it'.

But no hint of as to why. Well? What will it damage at the water treatment plant? What affect will it have except for, perhaps, giving the place a mildly pleasant hint of an odour of good coffee? (and god knows, those places need something...

So. What will it damage? What harm can it do? Is there a good reason not to put it in the rubbish or the sink? I'm not looking for personal opinion, as much as scientific fact and demonstration of 'bad things' (tm) one way or the other.

posted by Brockles to Food & Drink (9 answers total) 2 users marked this as a favorite
The water treatment plant is good at cleaning out some things and not others. Filtering out the solid bits is not so hard but remember what the grounds did to the water you just took them out of. Keeping the water (lakes, rivers, etc.) clean works best when you avoid putting stuff into it in the first place.
posted by winston at 6:05 PM on September 11, 2007

An acquaintance once told me that caffeine was the most frequently occurring contaminant in groundwater. This report, about the increase of pharmaceuticals within in the U.S. water supply, found caffeine to be "the highest-volume pollutant" in streams.

The USGS Toxic Substances Hydrology Program's information on Emerging Contaminants in the Environment would probably give you the scientific information you're seeking.
posted by truenorth at 6:31 PM on September 11, 2007 [1 favorite]

We ended up with a plugged sink, due in part to coffee grounds. But we use a french press, and so the grounds aren't in a convenient paper basket for disposal! We bought (from Roto-rooter) a bottle of this. It really does eat all the organic stuff that goes down the drain (over time, it's a collection of hungry bacteria).
posted by TeatimeGrommit at 6:45 PM on September 11, 2007

They just took the sink apart at our office - it took three days. The entire grease trap (a box about 1' x 1') was filled with used coffee grounds.

There is now a sign asking people to not was their coffee grounds down the sink.
posted by true at 6:50 PM on September 11, 2007

I actually read somewhere (in this book, I believe, although it was at someone else's house, so I can't check my reference) that coffee grounds can help to keep a drain clog-free. I've been washing coffee grounds down the sink for a few years now, with no clogs whatsoever. Granted, they're from a percolator and we make weak coffee, so YMM-particularly-V.

And, if you're washing things like coffee grounds down the drain, it's probably even more important to avoid washing things like grease down the drain.
posted by paleography at 7:55 PM on September 11, 2007

The best possible place for coffee grounds is a compost bin. Reuse it.
posted by pmbuko at 8:31 PM on September 11, 2007

I, too, have heard the second best thing to do with coffee grounds (after composting) is to put them down the drain, because they happily pick up the grease on the way down, thereby preventing clogs. I've been doing it for several years. No clogs.
posted by M.C. Lo-Carb! at 7:47 AM on September 12, 2007

If you don't compost, you can just dump the grounds at the base of any acid-loving plant, like roses or rhododendrons.
posted by rikschell at 8:57 AM on September 12, 2007

The fact that caffeine is such a contaminant is interesting, but if it doesn't go down the sink, it just goes to landfill, where the caffeine will get into the water table eventually anyway. So as an argument for not doing it, it just delays it, doesn't it?


I wonder how much caffeine naturally occurs in the water around coffee plantations? If the beans aren't harvested and drop to the ground and rot, does caffeine get into the water system anyway?
posted by Brockles at 9:23 AM on September 12, 2007

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