The water you brew with matters

Coffee is more than 98% water. The beans contribute flavor, aroma, and body. Water is the solvent that carries all of it to your mouth. If the water is wrong, the extraction is wrong, and the cup is wrong regardless of how good the beans are or how carefully you brewed.

Most people who pay attention to coffee spend time on grind size, water temperature, and brew ratios, and very little time on what is actually in the water. That is an oversight, and a fixable one.

What minerals do in a brew

Water is not just H2O when it comes out of your tap or your bottle. It contains dissolved minerals, primarily calcium, magnesium, bicarbonate, and sodium. These minerals affect coffee extraction in different ways.

Magnesium is particularly efficient at attracting and binding with coffee's flavor compounds. Water with moderate magnesium tends to produce a brighter, more expressive cup.

Calcium also contributes to extraction but in a slightly different way. It tends to produce a fuller, more rounded cup compared to magnesium-dominant water.

Bicarbonate (measured as alkalinity) acts as a buffer that neutralizes acidity. High bicarbonate softens or mutes the acidity in your cup. In a coffee you want to taste bright and acidic, this is a problem. In a darker or more bitter coffee, a little buffering can round out harsh edges.

Sodium is generally unwanted in brewing water except in very small amounts. At high levels it produces a flat or salty character.

The total of all dissolved minerals in your water is measured as Total Dissolved Solids (TDS), expressed in parts per million (ppm) or milligrams per liter (mg/L).

What the SCA recommends

The Specialty Coffee Association has published water quality standards for brewing. The targets are:

• TDS: 75 to 150 ppm, with 150 ppm as the ideal midpoint
• Calcium hardness: 50 to 175 ppm as CaCO3, target around 68 ppm
• Total alkalinity: around 40 ppm as CaCO3
• pH: 6.5 to 7.5, neutral
• Sodium: below 10 ppm
• Chlorine: zero

Most tap water in Western cities falls somewhere in this range but rarely hits the ideal. Soft-water cities like London (once filtered) and Copenhagen tend to be at the low end of TDS. Hard-water cities like Vienna or parts of the US Midwest run higher, sometimes above 200 ppm.

Why distilled water does not work

Distilled water has a TDS of roughly zero. No minerals, no dissolved solids. You would expect this to be neutral and produce a clean cup. It does not. With no minerals present, water cannot carry coffee's flavor compounds efficiently. The extraction is weak and the cup tastes flat and lifeless. Some extraction enthusiasts use near-distilled water and add minerals back in precise amounts to hit a specific target. This is accurate but requires effort and equipment.

For practical purposes, avoid distilled water. It produces worse coffee than good tap water.

Which bottled water works

If your tap water tastes strongly of chlorine or has TDS above 300 ppm, bottled water is worth trying. The goal is water in the 75 to 150 ppm TDS range with low bicarbonate and no chlorine.

Bottled waters that consistently perform well for brewing coffee include:

• Volvic (France): TDS around 130 ppm, low sodium, good mineral balance. Widely cited by baristas as a reliable reference water.
• Evian: Higher TDS (around 300 ppm) and higher calcium than ideal. Works better for espresso than filter. Not ideal for light-roast pour-overs.
• Acqua Panna: TDS around 200 ppm. Works reasonably well for both filter and espresso.
• Waitrose own-brand still (UK): Low TDS, good for soft-water brewing targets.

You do not need to buy expensive water to brew well. If your tap water is in the 75 to 200 ppm range and tastes neutral, use it. A simple TDS meter costs around ten dollars and will tell you your tap water's baseline in thirty seconds.

A practical starting point

If you want to improve your water without building a mineral stack:

1. Buy a Brita or similar carbon filter pitcher. This removes chlorine and reduces some excess minerals. TDS will drop slightly.
2. Test the filtered water with a TDS meter.
3. If TDS is below 70 ppm, add a pinch of Epsom salts (magnesium sulfate) per liter, roughly 0.2 to 0.4 grams. This adds magnesium without raising hardness significantly.
4. If TDS is above 200 ppm and the cup tastes flat or muted, dilute with filtered water or switch to Volvic.

Water chemistry is a depth-unlimited rabbit hole. The point is not to become an expert in it before you brew your next cup. The point is to understand that water is an active ingredient, and that small adjustments can produce noticeable changes in the cup without touching any other variable.