The SCA Water Standard

The SCA water standard is the Specialty Coffee Association’s set of targets for the water you brew and taste coffee with: how hard it should be, how much alkalinity it should carry, its pH and what it shouldn’t contain. There are two versions in circulation, and many websites mix them up. This page sets out both, in plain English.

The short version

• No chlorine, and no smell or colour.
• Calcium hardness 50–175 ppm (as CaCO3) in the 2024 standard; 17–85 mg/L in the 2009 one.
• Alkalinity at or near 40–70 ppm, the most important number for taste.
• pH 6 to 8 (2024), or 6.5–7.5 with a target of 7 (2009).
• Espresso can take more alkalinity and less hardness, SCA-published research suggests.

What does the current SCA standard say?

The SCA’s Standard 102-2024, part of its Coffee Value Assessment, sets the water for cupping. Whenever possible, cupping water should fall within these ranges:

Characteristic	Acceptable range
Chlorine	None
Calcium hardness	50–175 ppm as CaCO3
Alkalinity	At or near 40–70 ppm as CaCO3
pH	6–8

Source: SCA Standard 102-2024, Table 2. It replaces the older “Cupping Water” heritage standard.

ppm as CaCO3 sounds odd: it means “the amount of calcium carbonate that would give the same effect”. It lets hardness and alkalinity be compared on one scale, Jonathan Gagné explains on his Coffee ad Astra blog.

What did the 2009 standard say?

Many charts online still show the SCAA’s Water for Brewing Specialty Coffee standard, revised in November 2009:

Characteristic	Target	Acceptable range
Odour	Clean, fresh, odour-free
Colour	Clear
Total chlorine	0 mg/L
Total dissolved solids (TDS)	150 mg/L	75–250 mg/L
Calcium hardness	68 mg/L (4 grains)	17–85 mg/L (1–5 grains)
Total alkalinity	40 mg/L	At or near 40 mg/L
pH	7.0	6.5–7.5
Sodium	10 mg/L	At or near 10 mg/L

Source: the 2009 standard, as summarised in an SCA Q Grader study guide. The target is the ideal point; anything inside the range meets the standard.

Why do websites give different numbers?

Because they quote different versions, or round them. A sample of what you’ll find:

Source	Hardness	Alkalinity	pH	TDS
SCA Standard 102-2024	50–175 ppm (calcium)	40–70 ppm	6–8	Not set
2009 SCAA standard	17–85 mg/L (calcium)	Near 40 mg/L	6.5–7.5	75–250 mg/L
Pact Coffee	50–175 ppm (calcium)	40–75 ppm	6.5–7.5	150–175 ppm
Redber Coffee	50–175 ppm (total)	40–80 mg/L	6.5–7.0 ideal	Not given

Sources as listed. When in doubt, use the SCA’s own current document: no chlorine, hardness 50–175 ppm, alkalinity near 40–70 ppm.

Why does each number matter?

• Chlorine has to go because it can react with coffee compounds and leave medicinal off-flavours, the Q Grader guide notes.
• Hardness (calcium and magnesium) helps pull flavour out of the coffee. Observations cite a tendency to over-extracted flavours above about 250 ppm and under-extracted flavours below about 40 ppm, though measurements suggest hardness barely changes overall extraction between 20 and 250 ppm, Marco Wellinger of ZHAW writes in the SCA’s 25 Magazine.
• Alkalinity, mostly bicarbonate, neutralises the coffee’s acids. Too much and the cup tastes flat; this is why the SCA asks for a narrow range near 40 ppm, Gagné says.
• pH matters far less than alkalinity. As long as pH is roughly neutral (6–8) and alkalinity above 20 ppm, alkalinity’s effect on the cup’s acidity is several hundred times greater, Wellinger writes.

Does the standard work for espresso?

Not directly. Espresso uses roughly a tenth as much water per gram of coffee as filter, so the water’s alkalinity has much less coffee acid to neutralise, Wellinger explains. Simply scaling the filter standard up for espresso would cause heavy scale in the machine, so the SCA’s standards committee is working on a unified standard. The research he describes suggests espresso water can go as low as 20 ppm total hardness and as high as 150 ppm alkalinity while avoiding scale and corrosion.

How do you meet the standard?

Find out what’s in your water first: your local water supplier can tell you its hardness, and aquarium test kits for hardness (GH) and alkalinity (KH) work at home, Gagné suggests. Then either filter it, blend it with distilled water, or build your own water from scratch. See water hardness for coffee and DIY coffee water recipes.

Water and other guides

• Water hardness for coffee: what hard water does and how hard yours is.
• DIY coffee water recipes: make SCA-style water from distilled water and minerals.
• Coffee grind size chart: the other variable that changes extraction.