Very important — coffee is over 98% water. Water that is too hard mutes flavors and calcifies machines; water that is too soft tastes bland. Even a simple pitcher filter makes a noticeable difference in the cup.

How important is water quality for good coffee?

Very important — coffee is over 98% water. Water that is too hard mutes flavors and calcifies machines; water that is too soft tastes bland. Even a simple pitcher filter makes a noticeable difference in the cup.

Why that is

The numbers are clear: an espresso is 90–92% water, a filter coffee 98–99%. Water isn’t just a solvent — it’s the main ingredient. And like any main ingredient, its quality determines the result.

Three properties of water influence coffee flavor:

Total Hardness (Mineral Content). Minerals like calcium and magnesium help dissolve flavor compounds from the coffee grounds. Too few minerals (soft water) leads to under-extraction — the coffee tastes thin and bland. Too many minerals (hard water) mask the delicate coffee aromas and make the cup flat and muddy. The sweet spot, according to the SCA, is 50–175 ppm total hardness.

Carbonate Hardness (Buffer Capacity). Carbonate hardness neutralizes the acids in coffee. Too much carbonate hardness makes the coffee dull and devoid of acidity — the lively fruitiness gets lost. Too little lets the acidity dominate, and the coffee tastes harsh and sour. Ideal: 40–70 ppm.

pH Level. Ideally neutral (pH 7). Acidic water unnaturally amplifies coffee acidity, while alkaline water neutralizes it.

In Germany, average water hardness is around 16 °dH — well above the ideal range. In Berlin, it varies by district between 14 and 22 °dH. Anyone using untreated Berlin tap water for coffee is sacrificing aroma and shortening the lifespan of their machine.

The easiest entry point is a pitcher filter (Brita, BWT). It reduces hardness and removes chlorine. It’s not perfect, but for most home users, it’s a huge step forward. Those wanting to take the next step use professional under-sink filters or mix distilled water with mineral concentrates (like Third Wave Water).

A simple test: brew the exact same coffee once with tap water and once with filtered water. In most German cities, the difference is immediately obvious to the taste.

In practice at Green Wall Coffee

At Sophienstraße 27, we use filtered water for all our brewing methods. Water treatment was one of our first investments after opening — even before upgrading the espresso machine. To guests asking for the “one trick” for better coffee at home, I say: filter your water. It costs little and brings huge returns.

Related questions

• What is the ideal water hardness for coffee?
• Do I need a water filter for my coffee machine?
• What is the optimal water temperature for brewing?

You can find more in-depth information in the article How to make perfect espresso. Or drop by Sophienstraße 27 — Mon–Fri 8am–5pm, Sat 10am–5pm.