# Coffee Water Chemistry: Why H₂O is the Most Overlooked Ingredient
Coffee is 98-99% water. Yet the mineral composition of that water is the most overlooked quality factor in the entire specialty coffee chain. The same Ethiopian single-origin coffee extracted with London tap water versus SCA-optimized water can taste like two completely different coffees. Our SCA coffee water calculator lets you formulate perfect brewing water from scratch using common mineral salts and distilled water.Why does water mineralization matter so much?
GH (General Hardness): The sum of Magnesium and Calcium ions determines the water capacity to dissolve coffee flavor compounds.
KH (Carbonate Hardness): Bicarbonate concentration controls pH during extraction. Low KH produces sour coffee; high KH makes it flat.
Repeatability: Municipal water changes by season and location. Mineralized water is constant and reproducible batch after batch.
Equipment protection: Correct mineral levels prevent both corrosion (too-pure water) and limescale buildup (too-hard water).
# The SCA Standard: Technical Limits for Perfect Brewing Water
| Parameter | Minimum | SCA Ideal | Maximum |
|---|---|---|---|
| Total Hardness (GH) | 50 mg/L | 68 mg/L | 175 mg/L |
| Alkalinity (KH) | 40 mg/L | 40 mg/L | 70 mg/L |
| pH | 6.5 | 7.0 | 7.5 |
| TDS | 75 mg/L | 150 mg/L | 250 mg/L |
# Magnesium vs Calcium: The Mineral Battle That Defines Your Cup
Not all minerals behave the same way with coffee. Researcher Christopher Hendon demonstrated that magnesium forms ligands with complex volatile flavor molecules, extracting fruity and floral notes more efficiently. Calcium extracts heavier compounds, delivering body and silky mouthfeel but with less aromatic brightness.Professional barista rule of thumb
For espresso machines with brass or copper boilers, never use profiles with KH below 40 mg/L continuously. Very pure water is corrosive long-term. For filter methods (V60, Chemex, AeroPress) there is no boiler to protect, so you can safely use delicate profiles like Melbourne without concern.