15.2 Water Standards for Cupping & Brewing

A cup of brewed coffee is overwhelmingly water, so the minerals in that water shape extraction and taste. Q Graders meet two different SCA water specifications. Know which one applies.

Cupping water under SCA-102

SCA-102 section 7.4 says water for cupping should, whenever possible, fall within the acceptable range in its Table 2:

This is the specification inside the CVA standards, so it is the one to use for Q Grader cupping questions.

The 2009 SCAA brewing water standard

The SCAA's "Water for Brewing Specialty Coffee" standard, revised in November 2009, sets targets and acceptable ranges for brewing water:

TDS in this standard is based on a "4-4-2" conductivity conversion. The target is the most desirable point, but any value inside the acceptable range meets the standard.

Comparing the two

ppm and mg/L are equivalent for dilute water.

Hardness and alkalinity

Hardness measures dissolved calcium and magnesium. These ions help pull flavor compounds out of the grounds, so very soft water, such as distilled or pure reverse-osmosis water, tends to brew thin, flat, or sharp coffee.

Alkalinity measures acid-neutralizing capacity, mainly bicarbonate. Bicarbonate reacts with acids in the brew:

$\text{H}^+ + \text{HCO}_3^- \rightleftharpoons \text{H}_2\text{CO}_3 \rightleftharpoons \text{H}_2\text{O} + \text{CO}_2$

So alkalinity buffers perceived acidity. Too much makes bright coffees taste flat and chalky. Too little leaves acidity sharp and unbalanced.

Hardness and alkalinity are both reported "as CaCO3," which makes the numbers comparable, but they measure different things. Water can be hard with low alkalinity, or soft with high alkalinity.

Sensory effects of water problems

Chlorine reacts with phenolic compounds to form chlorophenols, which are smelled at extremely low levels as medicinal or antiseptic notes. That is why both standards call for no chlorine. A medicinal or phenolic note caused by tap water could mislead a cupper into marking a "phenolic" defect that is really a water problem. Test your water before blaming the coffee.

Testing cupping water

1. Chlorine — use a test kit or strips, since even small amounts matter.
2. Total hardness and calcium hardness — titration kits or a laboratory test.
3. Alkalinity — titration kit.
4. pH — calibrated meter.
5. TDS — conductivity meter, noting the conversion factor it uses.

Record results in your cupping log. If water changes, for example with a new filter cartridge, retest before the next session.

Building compliant water

Labs often start from reverse-osmosis water and add minerals back. Others use filtration that reduces chlorine and adjusts hardness and alkalinity. Whatever the method, the goal is simple: water inside the SCA-102 acceptable range for cupping, measured rather than assumed.

Calcium and magnesium

Both calcium and magnesium contribute to hardness. A 2014 computational study by Hendon and colleagues in the Journal of Agricultural and Food Chemistry modeled how dissolved cations bind coffee compounds and suggested that magnesium binds many of them more strongly than calcium. Some brewers use this to justify magnesium-rich mineral recipes. Calcium also contributes to limescale in heated equipment when bicarbonate is present. For cupping, though, the measurable target is the SCA-102 range, not a particular calcium-to-magnesium ratio.

A worked water check

A lab tests its filtered tap water:

The water fails on alkalinity, so the lab should expect muted acidity in its cuppings. Blending with reverse-osmosis water to bring alkalinity into range, then retesting, would be a sensible fix. Measured against the 2009 brewing standard, the same water would also miss its calcium hardness range of 17–85 mg/L.