Coffee Brew Water TDS Target Calculator
Calculate ideal brew water hardness and TDS for coffee.
Compare your tap water TDS against SCA standards and adjust with bottled or filtered water.
Brew Water TDS for Coffee
Water makes up 98%+ of coffee — its mineral content (TDS, hardness) directly affects extraction efficiency, sweetness, and clarity.
Specialty Coffee Association (SCA) standards:
| Parameter | Target | Acceptable Range |
|---|---|---|
| Total Dissolved Solids (TDS) | 150 mg/L | 75-250 mg/L |
| Calcium hardness (as CaCO₃) | 68 mg/L | 17-85 mg/L |
| Total alkalinity | 40 mg/L | 25-80 mg/L |
| pH | 7.0 | 6.5-7.5 |
| Sodium | 10 mg/L | 0-30 mg/L |
| Chlorine | 0 mg/L | 0 mg/L |
Why minerals matter:
- Calcium binds to coffee compounds → extracts flavor better
- Magnesium binds even more strongly → extracts more aromatic compounds
- Bicarbonate / alkalinity buffers acidity → too much mutes brightness
- Sodium is neutral → contributes texture without flavor binding
The “Sweet Spot” rule:
- Around 150 ppm TDS with balanced calcium/magnesium hardness = best extraction for most coffees
- Below 50 ppm: under-extracts, coffee tastes weak and watery
- Above 250 ppm: over-extracts and tastes muddy or bitter
Common water sources:
| Source | Typical TDS | Notes |
|---|---|---|
| Distilled / RO | 0-10 ppm | Too soft, extracts poorly |
| Most tap water | 50-300 ppm | Highly variable; chlorine bad |
| Filtered tap (Brita) | 30-150 ppm | Better, depends on filter age |
| Crystal Geyser | 60-160 ppm | Generally good for coffee |
| Volvic | 100-130 ppm | Good for light roasts |
| Evian | 320 ppm | Too hard for coffee, bitter |
| San Pellegrino | 950 ppm | Way too hard |
| Aquafina | <20 ppm | Too soft |
| “Third Wave Water” mix | ~150 ppm tuned | Designed for coffee |
DIY low-mineral water for coffee:
- Start with distilled or RO water
- Add packaged mineral mixes (Third Wave Water, Lotus) per gallon
- Or DIY: dissolve 1.45 g Epsom salt and 0.45 g baking soda in a gallon of distilled
- That gives roughly 155 ppm hardness and 70 ppm alkalinity, both as CaCO₃
Worth pausing on those two numbers, because they are more than double the SCA targets of 68 and 40. That is deliberate: this is the widely-shared extraction-boosting recipe, not the SCA midpoint, and it suits light roasts that need help. Halving both salts lands you on the standard instead. Do not confuse the 150 ppm TDS target with a 150 ppm hardness figure. They are different measurements and the coincidence of the number causes no end of trouble.
Light roast vs dark roast preferences:
- Light roasts: lower bicarbonate (preserves brightness): 30-50 mg/L
- Dark roasts: higher bicarbonate OK: 60-100 mg/L (smooths out edge)
Espresso machine note: Hard water (above 100 ppm hardness) scales heating elements. Use softened water or descaler regularly. Soft water (below 30 ppm) corrodes copper boilers — there is a sweet spot for machine longevity AND brew quality.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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