Why water matters
Brewed coffee is about 98% water. The minerals in that water decide how much flavor gets pulled out of the beans, which notes come through loud, and which stay quiet.
You don't need to memorize chemistry. Try a few recipes, taste what changes, and the rest builds up naturally.
What each mineral does
Two shorthand terms you'll see across the site: GH (general hardness: calcium plus magnesium combined) and KH (alkalinity: how strongly the water buffers acids). Most recipes are mostly about adjusting these two numbers.
Basic principles
- Start with distilled or RO water. It's a blank canvas. You can't subtract minerals from tap water, only add to it, so beginning from zero is the only way to really control what's in the cup.
- Use a 0.01g scale. Mineral doses are small: usually fractions of a gram per liter. A kitchen scale that only reads whole grams won't get you there.
- Typical filter targets: GH 50–150 mg/L, KH 30–80 mg/L (both measured as CaCO₃, which is the unit used across this calculator).
- Espresso usually runs lower alkalinity to keep brightness in the cup. Espresso is already concentrated; heavy buffering can dull the acidity that makes it interesting.
- Change one thing at a time. If you swap water and also change the beans, the grind, and the dose, you won't know what made the difference. Keep everything else steady while you dial in water.
Try it: RAsami Week 1
Robert Asami (a.k.a. RAsami) put together a 7-day filter series designed exactly for this: one recipe per day, each varying the balance of minerals against a fixed baseline. By day seven you'll have a feel for how calcium and magnesium trade off, and how alkalinity shifts the picture.
The exercise:
- Use the same beans and the same brew ratio every day.
- Brew one RAsami recipe per day.
- Keep a one-line note: what was different? More body? More brightness? Flatter? Sharper?
All seven recipes are already in the library.
Brewing a pour-over
If you're new to pour-over, here's a reliable starting point for a V60 or similar cone dripper:
15g coffee : 250g water (1:16.6 ratio)
Medium-fine grind (about the texture of table salt)
93°C water (just off boil)
Bloom: 45g of water, wait 30 seconds
Then pour in 2–3 steady streams to finish by about 2:30 total
- Ratio controls strength. More water per gram of coffee = weaker; less water = stronger.
- Grind controls how fast water flows through. Finer runs slower and extracts more, which lands as sweet or bitter depending on how far you push it.
- Temperature affects extraction speed. Hotter extracts faster; 93°C is a safe default across most roasts.
- The bloom lets CO₂ escape so water can actually contact the coffee evenly on the main pours.
Want a walkthrough? James Hoffmann's V60 technique is the most-shared starting point.
Brewing an espresso
Espresso has more moving parts than pour-over, but a starting recipe is straightforward:
18g coffee in → 36g espresso out (1:2, a "normale" shot)
Fine grind (usually finer than you expect, adjusted until flow hits the target time)
~93°C group temperature
25–30 seconds total pull
- Ratio. 1:2 is a balanced default. Shorter (1:1.5, "ristretto") concentrates everything; longer (1:3, "lungo") stretches the shot and can over-extract.
- Grind is the main lever. Shot running too fast and gushing? Grind finer. Dripping out way too slowly? Grind coarser.
- Freshness matters more than you'd think. Coffee past ~30 days off roast loses crema and drama, even when it still tastes fine on paper.
Want a walkthrough? James Hoffmann's dialing-in guide is a good first watch.
Next steps
You're ready to try it. Three places to go from here: