Why Water Matters
Water isn't just a neutral solvent. The minerals dissolved in water directly affect how coffee compounds extract and how they taste.
The same coffee brewed with different water can taste completely different. Soft water (low minerals) produces flat, dull coffee. Very hard water (high minerals) can taste chalky or metallic. Balanced mineral water creates clarity and complexity.
Key Insight
If you've dialed in grind, temperature, and ratio but coffee still tastes "off," water composition is often the culprit.
Mineral Content
Water contains dissolved minerals, primarily calcium (Ca²⁺) and magnesium (Mg²⁺). These minerals affect extraction in two ways:
- •Calcium and magnesium bind to coffee compounds and pull them into solution, enhancing extraction.
- •Bicarbonate (HCO₃⁻) acts as a buffer, neutralizing acids and reducing perceived brightness.
The Role of Key Minerals:
Calcium (Ca²⁺)
Enhances extraction of fruity, acidic compounds. Improves sweetness and clarity. Target: 20-80 mg/L.
Magnesium (Mg²⁺)
Binds to heavier, earthy compounds. Adds body and mouthfeel. Preferred by many specialty roasters. Target: 10-30 mg/L.
Bicarbonate (HCO₃⁻)
Buffers acidity. Too much makes coffee taste flat and dull. Target: 30-60 mg/L.
Sodium (Na⁺)
Enhances sweetness at low levels (<10 mg/L). Above 20 mg/L, water tastes salty.
Hardness and Alkalinity
Two terms dominate water chemistry discussions:
General Hardness (GH)
Total dissolved Ca²⁺ and Mg²⁺
Controls extraction efficiency. Higher hardness = more extraction. SCA recommends 50-175 mg/L CaCO₃ equivalent.
Total Alkalinity (KH)
Buffering capacity (bicarbonate)
Controls perceived acidity. Higher alkalinity = more acid neutralization = flatter coffee. SCA recommends 40-70 mg/L CaCO₃ equivalent.
The balance between hardness and alkalinity is critical. You want enough hardness for extraction but low enough alkalinity to preserve brightness.
Practical Solutions
Most home brewers don't have access to water testing equipment. Here are practical approaches:
1. Use Filtered Water
Carbon filters (like Brita) remove chlorine and some impurities but don't change mineral content much. Good baseline solution for most tap water.
2. Try Bottled Water
Different brands have different mineral profiles. Experiment with a few:
- •Crystal Geyser: Low minerals, good for light roasts
- •Volvic: Balanced profile, works well for most coffees
- •Avoid distilled: Zero minerals, produces flat coffee
3. Third Wave Water / Custom Recipes
Mineral packets or DIY recipes designed specifically for coffee. You add them to distilled water to create ideal brewing water.
Popular DIY recipe (Barista Hustle): Add small amounts of magnesium sulfate (Epsom salt) and potassium bicarbonate to distilled water. Precise, but requires weighing milligrams.
4. Remineralization Filters
Specialty filters (like BWT or Peak Water) that strip water and add back controlled minerals. More expensive but consistent results.
Simplest test: Brew the same coffee with tap water and bottled water side-by-side. If bottled water tastes significantly better, your tap water is limiting your coffee quality.