Coffee brewing water

Coffee is about 98% water, so the water you brew with isn't a background detail — it's most of the cup. Two waters can turn the same beans and the same technique into two noticeably different coffees. This is chemistry you can control.

The two levers that matter

• Hardness (mostly magnesium and calcium) pulls flavor compounds out of the grounds during extraction. More hardness, more extraction — up to a point. Magnesium in particular is prized for pulling bright, fruity notes.
• Alkalinity / buffer (bicarbonate) neutralizes coffee's natural acids. Some buffer keeps a cup from tasting sharp; too much flattens it and mutes the good acidity you actually want.

Great brewing water is a balance between these two: enough hardness to extract, enough buffer to smooth, not so much of either that the cup goes dull.

The target

The Specialty Coffee Association publishes a widely used target for brewing water. In round numbers, aim for a total hardness around 50–70 mg/L (as CaCO3) and an alkalinity around 40 mg/L (as CaCO3), with a roughly neutral pH. You don't need to hit it to the decimal — getting into the neighborhood is most of the benefit.

The easy home method: build from distilled

The most repeatable approach is to start from a blank canvas (distilled or RO water) and add minerals back to a known target. This removes the guesswork of whatever your tap happens to be doing that day.

A common enthusiast approach uses two simple "concentrate" solutions:

• A magnesium concentrate — Epsom salt (magnesium sulfate) dissolved in a small amount of distilled water.
• A buffer concentrate — baking soda (sodium bicarbonate) dissolved in distilled water.

You then add a measured amount of each concentrate per liter of distilled water to hit the hardness and buffer targets. Working from concentrates is far easier than trying to weigh tiny pinches of dry powder per liter.

Prefer not to mix chemistry? Commercial mineral packets made for coffee (added to distilled water) hit similar targets and are the no-fuss route.

Tasting your way in

• Cup tastes flat or hollow → not enough hardness; add more magnesium concentrate.
• Cup tastes sharp or sour → not enough buffer; add a little more bicarbonate.
• Cup tastes dull or "muddy," acidity muted → too much buffer; pull the bicarbonate back.
• Bright and fruity is the goal → favor magnesium over calcium in your hardness.

Why bother

If you've invested in good beans and a decent grinder, water is the cheapest remaining upgrade — and often the most dramatic. A café-quality bean brewed in flat, over-buffered tap water can taste ordinary; the same bean in properly built water can taste like what you paid for.

---

Use only food-grade minerals. This is a guide for brewing, not for daily drinking water — brewing water targets aren't the same as ideal drinking-water mineral levels.