You can read a water label and still not know whether that water is good for coffee.
A label might show TDS, pH, calcium, and magnesium, but not alkalinity. Or it shows alkalinity but not total hardness. Or everything looks reasonable on paper, but you have no way to weigh which numbers actually matter most.
That's the gap this post addresses. Not just what good water looks like, but how to score it, so you can compare any two waters and know which one is better for brewing.
Why a single number isn't enough
The Specialty Coffee Association's Water Quality Handbook identifies alkalinity and total hardness as the two parameters that most directly drive flavor and extraction quality. pH matters for safety and balance. Sodium and TDS are secondary.
The answer is a weighted score.
The weighted scoring system
| Parameter | Weight | Why |
|---|---|---|
| Alkalinity | 50% | The dominant factor in flavor balance (controls how coffee's natural acids reach your palate) |
| Total hardness | 30% | Drives extraction (minerals pull flavor compounds from the grounds) |
| pH | 10% | Safety and equipment protection (rarely the problem, but important when it is) |
| Sodium | 8% | High concentrations slow extraction and add saltiness |
| TDS | 2% | Residual reference only (composition matters far more than the total) |
A water with alkalinity squarely in the 40-75 ppm range and good hardness will score well even if TDS falls outside the old SCAA 150 ppm target.
Ranges, not fixed targets
Within the ideal range, the score is at its maximum. Outside the range, the score drops, but gradually, without cliffs.
The balance rule: hardness must exceed alkalinity
Total hardness should always be greater than alkalinity.
When alkalinity exceeds hardness, the water's buffering capacity overpowers its extraction potential. The scoring system applies a proportional penalty when alkalinity exceeds hardness; the larger the imbalance, the larger the deduction.
What this looks like in practice
- Bicarbonate (HCO₃): this is your alkalinity proxy. Divide by 1.22 to convert to ppm as CaCO₃.
- Calcium (Ca²⁺) and Magnesium (Mg²⁺): these combine into total hardness. Multiply calcium by 2.5 and magnesium by 4.1, then add them.
- pH: usually listed directly.
- Sodium (Na⁺): listed in mg/L.
Scanning a label instead of calculating manually
The OCR feature in Café com Água uses your phone camera to read a water label and extract the mineral values directly. Point the camera at the composition table on the bottle, confirm the captured values, and the app scores the water in seconds.
A few things worth knowing about OCR label reading:
- Labels aren't standardized. Brands use different layouts, abbreviations, and units.
- Some labels list bicarbonate instead of alkalinity; the app handles the conversion.
- Curved bottles, reflections, and condensation can reduce accuracy.
What the score tells you (and what it doesn't)
A high score means the water's mineral profile aligns well with the SCA's parameters. It doesn't mean the water will taste great in every cup: brewing method, bean quality, grind, and temperature all interact with water chemistry.
Beyond scoring: the optimizer and blend calculator
The Optimizer calculates exactly how many drops of mineral solutions to add to bring your water to the center of the SCA ideal ranges.
The Blend Calculator simulates mixing two waters in any proportion. It calculates the resulting chemical profile (including pH, which combines logarithmically) and scores the blend.
Start with your label
Check alkalinity (40-75 ppm), total hardness (50-175 ppm, higher than alkalinity), pH (6.5-7.5), and chlorine (none detectable).
Café com Água scores water against SCA parameters: scan a label with your camera or enter values manually. Available free on Google Play.
Download Café com Água for free
Rate your water with a weighted SCA score. Optimizer and blend calculator included.
Café com Água