Coffee Chemistry / SCA Standards / Extraction

Water Chemistry for Coffee: The 98% of Your Cup

Water is not a passive solvent. Its dissolved calcium, magnesium, and bicarbonate ions act as the chemical agents that dictate which flavor compounds are extracted and which are lost.

Brew bar and brew water

Scientific fundamentals

Water as an active molecular extractor

In a filter coffee cup (V60, Chemex, French press), water makes up 98.5% of the total volume. In a dense espresso shot, water still accounts for 88% to 90%.

The soluble flavor compounds in roasted coffee (chlorogenic acids, caffeine, trigonelline, lipids, and caramelized sugars) are polar organic molecules. To be pulled out of coffee particles efficiently, they require positively charged mineral ions (Ca²⁺, Mg²⁺) that act as molecular "hooks."

The water challenge in Spain

Across much of the Iberian peninsula (especially Mediterranean regions and the south), municipal tap water is extremely hard (TDS higher than 400 ppm) with heavy chlorine and limescale. Brewing with it dulls high-scoring coffees and causes machine scale buildup rapidly.

Industry standards

The 5 water parameters according to the SCA

The Specialty Coffee Association (SCA) and chemist Christopher Hendon define target mineral ranges for balanced extraction:

TDS (Total Dissolved Solids)
75 – 150 ppm (mg/L)

Overall mineral concentration. Below 50 ppm yields hollow, weak cups; above 200 ppm crowds the solution and inhibits flavor extraction.

Magnesium Hardness (Mg²⁺)
20 – 40 ppm CaCO₃

The star extraction ion: its higher charge density bonds tightly with light oxygen-rich volatiles, accentuating bright florals and fruit acidity.

Calcium Hardness (Ca²⁺)
30 – 60 ppm CaCO₃

Contributes weight, body, and mouthfeel. Excess (>100 ppm) over-extracts astringency and creates limescale build-up in boilers.

Buffer Alkalinity (HCO₃⁻)
40 – 70 ppm CaCO₃

Buffers brew pH. High alkalinity (>100 ppm) neutralizes lively origin acidity; low alkalinity (<20 ppm) leaves coffee unpleasantly sour.

Optimal pH
6.5 – 7.5

Neutral window. Protects espresso boiler metal from corrosion while allowing organic bean acids to shine naturally.

Supermarket guide in Spain

Analysis of popular Spanish bottled mineral waters

We evaluated laboratory mineral reports and supermarket labels for common bottled waters available across Spain to assess real-world cup extraction performance:

Brand TDS (Residue) Calcium (Ca²⁺) Magnesium (Mg²⁺) Bicarbonates (HCO₃⁻) Barista Verdict
Lanjarón 150 mg/L 30 mg/L 14 mg/L 100 mg/L Excellent All-Rounder Well-balanced magnesium and calcium ratio. Great for pour-over filter (V60, AeroPress) and domestic espresso straight from the bottle.
Fuente Liviana 110 mg/L 28 mg/L 10 mg/L 85 mg/L Very Good for Filter Mild, clean mineralization. Delivers bright, clear cups with light and medium single-origin roasts.
Bezoya 28 mg/L 0.9 mg/L 0.3 mg/L 5 mg/L Ultra-Low Mineralization Ideal for dark roasts and delicate espresso boilers. For light-roast specialty coffee, it should be remineralized with mineral salts.
Nestlé Aquarel 190 mg/L 45 mg/L 12 mg/L 140 mg/L Acceptable for Body Higher buffer alkalinity. Highlights chocolate and nutty notes in moka pot or traditional espresso with milk.
Solán de Cabras 280 mg/L 60 mg/L 26 mg/L 285 mg/L Too High Alkalinity for Filter Elevated bicarbonate content acts as a heavy buffer, muting vibrant citric and malic acids in delicate coffees.

Home solutions

How to get optimal brew water at home

To avoid continuous single-use plastic bottles, three effective home treatment methods exist:

1. Magnesium Filter Pitchers (BWT): Unlike standard pitchers, BWT cartridges filter chlorine and exchange heavy calcium for magnesium (Mg²⁺), amplifying floral and fruit notes.

2. Reverse Osmosis with Remineralizer: Strips ~95% of dissolved solids from tap water and reintroduces a balanced mineral blend before dispensing.

3. Distilled Water + SCA Minerals: The gold standard for precision. Take pure demineralized water and dissolve measured packets like Third Wave Water or DIY food-grade mineral salts (Epsom magnesium and potassium bicarbonate).

Barista Hustle DIY Water Recipe (1 Liter)

For home baristas equipped with a 0.01g precision scale:

  • 1 Liter pure distilled water or Bezoya.
  • 0.17g Sodium Bicarbonate (NaHCO₃).
  • 0.41g Magnesium Sulfate heptahydrate (Epsom salts).
  • Result: 80 ppm hardness & 40 ppm alkalinity. Flawless SCA standard.

Frequently Asked Questions

Common questions about coffee water

Why does tap water often ruin specialty coffee?

In many parts of Spain and coastal Europe, municipal tap water has TDS higher than 400 ppm and heavy calcium hardness, which blunts coffee flavor and causes scale. Furthermore, disinfectant chlorine reacts with coffee phenols to create chlorophenols, giving a metallic, medicinal taste.

Which is better: a BWT magnesium filter pitcher or a standard Brita?

Standard Brita pitchers use hydrogen/sodium exchange resins that soften water but lower pH and remove magnesium. BWT pitchers exchange calcium for magnesium (Mg²⁺), enhancing volatile extraction and fruity aromatics in the cup.

Can I brew specialty coffee with pure distilled water?

No. Pure distilled water (0 ppm TDS) lacks the calcium and magnesium ions required to chemically bind and extract flavor compounds from coffee grounds, producing a sour, hollow, and weak extraction. Unbuffered pure water can also be corrosive to espresso machine metals.

What is Third Wave Water or mineral dosing?

It is the method of adding pre-measured packets of pure minerals (magnesium sulfate, calcium chloride, potassium bicarbonate) into distilled or reverse osmosis water to reproduce exact SCA chemistry standards consistently.