And a paper cup?
A conventional takeaway paper cup, with its plastic lid, takes about 0.54 litres to make.
1 reusable cup = 15 paper cups
On manufacturing water alone, your reusable cup pays for itself after 15 coffees. About three weeks of weekday coffee.
But that's not the end of the story. Every time you use it, you wash it.
Your cup, your habits
Set how you drink and how you wash. The answer changes more than you'd think.
Reusable cup, washed each time
A new paper cup each time
The water isn't in the cup. It's in how you use it. Wash it by hand under a running tap and, on water alone, a reusable cup may never catch up with paper.
That's not a reason to go back to paper. The same study found a reusable cup beats a paper cup on carbon within about 24 days, and on waste from the first coffee. Keep the cup, and wash it smarter: a full dishwasher, or a sink of water instead of a running tap.
Where the 8 litres go
Surprisingly, the glass isn't the biggest part. The cardboard box it's sold in took more water to make than the cup.
- Retail box: about 2.8 L
- Glass cup: about 2.0 L
- Silicone band: about 1.9 L (a cork band uses about 0.5 L)
- Lid and plug: about 0.7 L
- Transport and assembly: about 0.8 L
How we worked it out
We compared the water used to make each cup, plus the water used to wash the reusable one after every coffee. A paper cup is used once and thrown away, so its only cost is making it.
Numbers we used
- Reusable glass cup: 8 L, from adding up the parts reported in KeepCup's life cycle assessment for its 340 ml glass cup.
- Paper cup: 0.54 L for a conventional cup and lid, from an independent Intertek assessment covering tree growing to disposal.
- Dishwasher: 0.3 L per cup (15 L a load, 50 cups a load). Quick rinse: 0.5 L. Both from the KeepCup study.
- Running tap: about 1 L. This one is our own assumption: roughly 10 seconds under a typical kitchen tap. The study's 0.5 L rinse assumes about 2 seconds, which is optimistic.
Things to know
- Both studies were paid for by cup companies: KeepCup commissioned its study, and Frugalpac, which makes paper cups, commissioned the Intertek one.
- They may not count water the same way, so treat the break-even points as approximate.
- You may see claims that paper cups use 20 times more water. Figures like that usually count the rain that grows the trees. We left rainfall out, as we do for every item on our table.
- We haven't included the water used to make the energy that heats washing water, or the coffee itself.
Sources
- Edge Environment for KeepCup (2018, rev. 2023). Reusable coffee cups life cycle assessment and benchmark.
- Intertek for Frugalpac (2021). Life cycle assessment of single-use coffee cups, as reported by Frugalpac.
Why a water company cares
Your cup is a small version of a big problem. Factories use huge amounts of water to wash, rinse and cool things, and most of it goes down the drain after one use. Danu Water builds adaptive electromembrane separation systems that adjust in real time to the variability of industrial water and clean that water so factories can use it again.
If you'd like the occasional fact like this one, we send a short newsletter.
Get the newsletterFigures are estimates built from published life cycle studies and rounded. One cup icon holds 340 ml.