What water does Green Wall Coffee use for its coffee?
We treat Berlin tap water with a BWT reverse osmosis system. Around 430 ppm becomes 110 to 120 ppm with a raised magnesium content — our standard for brewing coffee.
Why Berlin water has to be treated
Berlin tap water sits at around 430 ppm of dissolved minerals — measured at the tap in Sophienstraße, and an entirely normal figure for Berlin. For drinking that is fine. For coffee it is too much.
Too hard means extraction runs incompletely, acids are buffered away, and the coffee tastes flat and dull. On top of that comes the practical damage: scale settles in the boiler and lines of the machine and costs more over time than any water system.
The value we run
The BWT reverse osmosis system first strips the water of nearly all minerals and then adds a defined mix back in. Our target is 110 to 120 ppm with a raised magnesium content.
Magnesium is not incidental: it makes the finer aromas come through more clearly — floral notes and fruit. The coffee reads as more brilliant and more complex. Calcium does something else: it mainly builds body. Water at the same ppm value but calcium-heavy tastes noticeably different in the same coffee.
This value applies to all our coffees alike — espresso and filter, house blend and single origin. The water is the one variable that stays constant while beans and roast profiles change.
What that means at home
A reverse osmosis system is overkill for domestic use. If you make coffee at home in Berlin, a simple jug filter already gets you noticeably further — it lowers hardness, even if not in a controlled way to a target value.
More important than the perfect number is doing anything at all: the difference between 430 ppm and around 150 ppm is bigger on the palate than the difference between two decent coffees.
In practice at Green Wall Coffee
At our café at Sophienstraße 27 in Berlin-Lichtenberg every espresso and every filter coffee runs on this treated water. If you want to know how large the difference is, try it at home: brew the same coffee once with filtered and once with unfiltered water.
Further reading
Related questions:
- Does Green Wall Coffee have a toilet and tap water?
- Can I buy coffee beans at Green Wall Coffee?
- What does a coffee cost at Green Wall Coffee?
Also relevant:
- Do I need a water filter for my coffee machine? — Water & Water Quality
- How do I measure water hardness myself? — Water & Water Quality
All questions in this topic: Green Wall Coffee in Detail