Water for specialty coffee
The coffee in your cup is, by weight, almost 99% water. Change the water and you literally change what the coffee can give.
An introductory guide, no jargon.
Why water matters more than it seems
That 99% of water pulls some coffee compounds better than others depending on the minerals dissolved in it. It's not magic — it's simple chemistry.
Very hard water tends to give flat, bitter cups. Water with nothing dissolved tends to give cups that are too sharp and bodyless. Between those two extremes lies fertile ground — and that's where good coffee water is built.
GH, KH and TDS explained without jargon
You'll see these initials in almost every water recipe. All three measure dissolved minerals, but each tells a different story.
GH · General hardness
Reflects how much calcium and magnesium there is. These are the minerals that most help extract sweetness and body from coffee.
KH · Alkalinity
Reflects how much bicarbonate there is. It acts as a brake: it softens acidity. High KH mutes fruity acidity; low KH lets it shine.
TDS · Dissolved solids
The total amount of minerals dissolved in the water, in mg/L (or ppm). A quick sense of how loaded the water is before it touches the coffee.
The minerals that move the cup
Magnesium
The most efficient ion at pulling sweetness and aromatics. Raise it for clarity; overdo it and you get a dry, bitter finish.
Calcium
Adds body and softens acidity, but extracts less than magnesium. It's the main cause of scale in machines and kettles.
Bicarbonate
This is alkalinity (KH). It neutralises acids: more bicarbonate softens acidity; less leaves it bright.
Water for filter vs water for espresso
Filter and espresso extract very differently. Filter: long time and low pressure, water passes through the bed by gravity. Espresso: short time and around 9 bar of pressure through a dense puck.
That's why they don't ask for the same water. For filter, moderate mineralisation brings clarity without masking delicate nuances. For espresso, a bit more body and bicarbonate is usually preferred, because the concentration in the cup is already high and the water needs to leave room.
Filter · V60, Chemex, Aeropress
Moderate mineralisation — clarity and lively notes.
Espresso
More body and bicarbonate — softer acidity.
Remineralisation: building your water
Remineralising means starting from water with almost no minerals — distilled or reverse osmosis — and adding small amounts of salts to build a specific profile. Starting from zero gives control and reproducible results cup to cup.
You don't need a lab: a 0.1 g scale and a few basic salts are enough to start. The idea is to raise GH and KH into a window that suits the coffee in front of you.
Exact amounts depend on the coffee and the method. In Atlas, the app calculates the recipe for you based on what you choose.
The tools live in the app
Build your water with Atlas
In the Atlas app you get a quick profile for a usable water in under a minute, a calculator to build your own to the gram, and a library to save and reuse what works for you.
- Quick water profile in under a minute
- Calculator with exact amounts per method
- Library to save and reuse your recipes
Free download for iPhone.