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Water for coffee at home: what the SCA standard actually says
By Chris Y. · Founder & editor
A cup of brewed coffee is about 98.6 percent water, so the water is not a detail. The numbers people quote for it come from the Specialty Coffee Association, and almost every article that quotes them gets something wrong — usually by mixing figures from two different SCA documents that do not agree with each other.
Here is the short version, from the source documents rather than from other guides. The SCA's 2018 Coffee Standards ask for calcium hardness of 50 to 175 ppm as calcium carbonate, alkalinity at or near 40 to 70 ppm, pH 6 to 8, and no chlorine. The older SCAA one-page water standard, revised 21 November 2009 and still the source of most of the numbers on the internet, asks for total dissolved solids of 150 mg/L in a range of 75 to 250, calcium hardness of 68 mg/L in a range of 17 to 85, alkalinity 40 mg/L, pH 7.0 in a range of 6.5 to 7.5, and sodium 10 mg/L.
Those two calcium hardness figures do not overlap in the middle. The 2009 target of 68 mg/L sits below the 2018 range's floor of 50 only in the sense that its own acceptable range — 17 to 85 — is mostly under it. If you have been told there is one authoritative SCA number for water hardness, there is not, and this page shows you both tables and what to do given that.
Questions people ask
What is the SCA's recommended water for coffee, in one line?
Calcium hardness between 50 and 85 ppm as calcium carbonate, alkalinity around 40 ppm, pH near 7, and no chlorine at all. That band satisfies both the 2018 SCA Coffee Standards (50–175 ppm hardness, pH 6–8) and the older 2009 SCAA water standard (17–85 mg/L hardness, pH 6.5–7.5), which do not otherwise agree.
Why do different articles quote different SCA water numbers?
Because the SCA has published two different tables. The 2009 SCAA one-page standard includes TDS (150 mg/L target, 75–250 range) and sodium (10 mg/L); the 2018 SCA Coffee Standards drop both rows and widen calcium hardness to 50–175 ppm and pH to 6–8. Most articles quote a mix of the two without saying so.
Can I use distilled water for coffee?
Not on its own. Distilled water has no calcium or magnesium, and those ions are what bind to and carry the flavour compounds out of the grounds — the result is a thin, hollow cup regardless of grind or ratio. Distilled water plus a measured mineral additive is a different matter, and it is the most repeatable water you can brew with.
Is softened water good for making coffee?
No. A conventional ion-exchange softener replaces calcium and magnesium with sodium, which removes the minerals extraction depends on and pushes sodium well past the 10 mg/L the 2009 SCAA table targets. It protects your plumbing and it makes worse coffee than the hard water it replaced.
Does a Brita-style filter jug make water that meets the SCA standard?
It reliably fixes the one thing both tables are absolute about — chlorine — and it does comparatively little to hardness or alkalinity. If your utility report shows hardness in the 50 to 175 ppm range, a carbon jug is likely all you need. If it shows 300 ppm, the jug helps the taste and does not bring you inside the standard.
How much water quality actually matters compared to the grinder?
Water sets the ceiling; the grinder decides whether you reach it. Chlorinated water will spoil a perfectly extracted cup, and perfect water will not rescue a grind that produces dust and boulders together. Fix chlorine first because it is nearly free, then fix the grinder, then worry about mineral content.
What TDS should coffee water be?
The 2009 SCAA standard targets 150 mg/L with an acceptable range of 75 to 250 mg/L. The 2018 SCA standards have no TDS row at all, which is a deliberate change: TDS is measured by conductivity and two waters with identical TDS can behave very differently depending on whether the dissolved solids are calcium or sodium. Treat it as a screening number rather than a target.
The two tables, verbatim
SCAA Standard, "Water for Brewing Specialty Coffee" — version 21NOV2009A
A single page published by the Statistics & Standards Committee of the Specialty Coffee Association of America. This is where the widely quoted "150 ppm TDS" figure comes from.
| Characteristic | Target | Acceptable range |
|---|---|---|
| Odor | Clean / Fresh, odor free | |
| Color | Clear color | |
| Total chlorine | 0 mg/L | 0 mg/L |
| TDS | 150 mg/L | 75 – 250 mg/L |
| Calcium hardness | 4 grains, or 68 mg/L | 1 – 5 grains, or 17 – 85 mg/L |
| 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 |
The document adds one footnote worth knowing: TDS measured based on a 4-4-2 conversion. That is a conversion factor a TDS meter applies between electrical conductivity and a dissolved-solids number, and it means two meters can disagree about the same glass of water.
SCA Coffee Standards, revised 2018 — §4.1 Water for Brewing Standards
The current-era document, published by the merged Specialty Coffee Association. It is shorter, and it drops two rows entirely.
| Characteristic | Target | Acceptable range |
|---|---|---|
| Odor | Clean / fresh, odor free | |
| Chlorine | None | None |
| Calcium hardness | 50 – 175 ppm CaCO₃ | 50 – 175 ppm CaCO₃ |
| Alkalinity | 40 ppm | At or near 40 – 70 ppm CaCO₃ |
| pH | 7.0 | 6 – 8 |
Note what has gone: there is no TDS row and no sodium row in the 2018 table. So the single most quoted coffee-water number in existence — 150 ppm TDS — comes from a 2009 document, not from the current standards. And the calcium hardness band has been raised and widened: from a 17 to 85 mg/L range around a 68 mg/L target, to a flat 50 to 175 ppm.
What the disagreement means in practice
It means two things, and neither of them is that the standard is worthless.
- There is a wide band that satisfies both documents. Calcium hardness between 50 and 85 ppm as calcium carbonate, alkalinity around 40 ppm, pH near 7, and no chlorine at all is inside both tables. That is the target to aim at if you want to be right by either measure.
- Precision past that band is not what is holding your coffee back. If your water is at 60 ppm hardness rather than 68, that is not the reason the cup tastes flat. Chlorine is, hardness in the hundreds is, and a grinder that produces dust and boulders in the same batch certainly is — see our dialling-in guide before you buy a water kit.
What each number is doing
- Chlorine — the one that is not negotiable. Both tables ask for none. Municipal water is chlorinated by design, and chlorine tastes like chlorine in a drink that is 98 percent water. This is the single highest-value change most people can make, and a basic carbon filter jug removes it.
- Calcium hardness. Calcium and magnesium ions are what actually bind to and carry flavour compounds out of the coffee. Too little and the cup is thin and hollow no matter how you brew it; too much and the brew tastes chalky and your kettle and espresso boiler scale up.
- Alkalinity. This is the buffering capacity — how strongly the water resists a change in pH. Coffee is acidic, so high-alkalinity water neutralises the acidity that makes a good cup bright and leaves it flat. Both tables converge on roughly 40 ppm, and the 2018 one allows up to 70.
- pH. The acceptable window widened from 6.5–7.5 to 6–8 between the two documents, which is the SCA acknowledging that pH matters less than the two numbers above it.
- TDS. Present in 2009, absent in 2018, and the reason is worth understanding: TDS is a proxy measured by conductivity, and two waters at the same TDS can behave completely differently depending on whether those solids are calcium or sodium. It is a useful screening number, not a target to chase.
How to find out what is in your water, for nothing
- Read your utility's annual water quality report. US water systems are required to publish one, and it typically lists hardness, alkalinity, pH, chlorine and TDS for your area. It is the most accurate free data you will get, and it takes five minutes to find.
- Compare it to the band above. Hardness between 50 and 85 ppm CaCO₃, alkalinity near 40, chlorine zero. If your hardness is in the hundreds — much of the US Midwest and Southwest is — you are outside both tables.
- Know the legal baseline is not a coffee baseline. The EPA's secondary drinking water standards are non-enforceable guidelines for taste and appearance, and they set TDS at 500 mg/L and pH at 6.5 to 8.5. Water that is perfectly fine to drink by that measure can be double the SCA's top acceptable TDS.
The four practical options, in order of cost
- A carbon filter jug. Removes chlorine and improves taste, does very little to hardness or alkalinity. If your water is already in a sensible hardness range, this is the whole job for very little money, and it is where everyone should start.
- Bottled spring water with a published mineral analysis. Many brands print calcium, magnesium, bicarbonate and TDS on the label. Pick one that lands in the band, and you have repeatable water with no equipment. It is the most expensive option per liter and the easiest to test with.
- Distilled or reverse-osmosis water plus a mineral additive. Start from nothing and add a measured packet or concentrate. This is the only approach that gives you the same water anywhere in the world, and it is what most competition brewers use. Distilled water on its own is a bad idea — with no calcium or magnesium there is nothing to carry the flavour, and the cup comes out hollow and flat.
- A plumbed filter or softener — with one warning. Conventional ion-exchange softeners swap calcium and magnesium for sodium. That prevents scale and it also removes the minerals coffee extraction depends on, while pushing sodium far past the 2009 table's 10 mg/L target. Softened water is worse for coffee than the hard water it replaced.
What this changes about buying equipment
Hard water is the reason a drip machine or an espresso boiler dies young: scale coats the heating element, the machine takes longer to reach temperature and then fails to hold it, and the brew drifts below the 90 to 96 °C that SCA Standard 310-2021 specifies. Every machine in our drip guide and our espresso guide has a descaling routine in its manual, and in water above about 175 ppm hardness that routine is a monthly commitment rather than an annual one.
It is also the cheapest upgrade nobody makes. A filter jug costs less than a bag of good coffee and changes every cup you brew for a year. A new brewer changes considerably less than that.
Sources
- SCAA Standard — Water for Brewing Specialty Coffee, revised 21 November 2009 (VERSION 21NOV2009A); mirrored copy, as the SCA no longer hosts the original page
- Specialty Coffee Association — Coffee Standards, revised 2018 (§4.1 Water for Brewing Standards; §5.1 Golden Cup)
- Specialty Coffee Association — Coffee Standards index
- SCA Standard 310-2021 — Home Coffee Brewers: Specifications and Test Methods (§6.2 brewing temperature 90–96 °C)
- US EPA — Secondary Drinking Water Standards: Guidance for Nuisance Chemicals (TDS 500 mg/L, pH 6.5–8.5)