Water for coffee, with the sources attached
What this is
Reference data on water chemistry for brewing coffee. Every number carries a named source document and the date it was checked. Where a figure is derived, the arithmetic is shown so you can check it rather than trust it.
17 pages · 15 sourced facts
Standards & data
The published figures, each with its source document and the date it was checked.
- What water should you use to brew coffee?Brew with water near 150 mg/L total dissolved solids and 40 mg/L alkalinity, containing no chlorine. Filtered tap water suits most people. Distilled and reverse osmosis water taste flat and corrode machines unless you add minerals back. Water above 120 mg/L hardness scales boilers and mutes acidity.
- What water quality does the SCA recommend for brewing coffee?The 2009 SCAA standard targets 150 mg/L total dissolved solids, accepting 75 to 250. It asks for 40 mg/L total alkalinity, 68 mg/L calcium hardness, pH 7.0 within a 6.5 to 7.5 band, sodium near 10 mg/L, and zero total chlorine.
- What water hardness causes limescale in an espresso machine?Scale forms when heated water deposits insoluble carbonates. The WHO calls water below 60 mg/L calcium carbonate soft, 60 to 120 moderately hard, 120 to 180 hard, and above 180 very hard. Espresso boilers scale fastest in the hard bands, well above the 40 mg/L alkalinity coffee brewing targets.
- How does the WHO classify water hardness?The World Health Organization classifies water below sixty milligrams per litre of calcium carbonate as soft, sixty to one hundred and twenty as moderately hard, one hundred and twenty to one hundred and eighty as hard, and above one hundred and eighty as very hard.
Glossary
One term per page, defined in a single extractable sentence.
- What is total alkalinity in water?Total alkalinity is the capacity of water to neutralise acid without its pH falling, conventionally expressed as milligrams per litre of calcium carbonate equivalent.
- What is total dissolved solids (TDS) in water?Total dissolved solids is the combined mass of all dissolved substances in water — minerals, salts and organic matter — reported in milligrams per litre.
- What is water hardness?Water hardness is the traditional measure of the capacity of water to react with soap, caused by dissolved polyvalent metallic ions — predominantly calcium and magnesium — and expressed as milligrams per litre of calcium carbonate equivalent.
- What is carbonate hardness?Carbonate hardness is the fraction of total hardness associated with carbonate and bicarbonate ions, which precipitates when water is heated. It is also called temporary hardness.
Comparisons
Head-to-head matrices rather than prose, so every cell is checkable.
- Distilled, reverse osmosis or filtered water for coffee — which should you use?Carbon-filtered tap water is the practical choice: it removes chlorine and leaves minerals intact. Distilled and reverse osmosis water strip almost everything, and the World Health Organization describes demineralised water as highly aggressive to metal. Use them only as a base you remineralise yourself.
- Is softened water or filtered water better for a coffee machine?Filtered water is better for the cup, softened water for the boiler. Ion exchange replaces calcium and magnesium with sodium, which protects against scale but pushes sodium far above the ten milligrams per litre brewing target. Carbon filtering removes chlorine and leaves hardness untouched.
How to
Numbered procedures with the arithmetic shown, not recipes to trust.
- How do you remineralise distilled water for coffee?Weigh 0.101 grams of Epsom salt and 0.067 grams of baking soda into one litre of distilled water, then stir until fully dissolved. That reaches ten milligrams per litre of magnesium and forty of alkalinity. Scale both figures linearly for larger volumes.
- How do you reduce limescale risk in an espresso machine?Find your water's alkalinity, then bring it toward forty milligrams per litre as calcium carbonate rather than toward zero. Blend hard supply water with distilled, or dose distilled water yourself. Avoid going fully demineralised, which trades scale for corrosion the World Health Organization warns about.
Questions
One narrow question answered directly, in the first paragraph.
- Does distilled water damage an espresso machine?Yes, it can. The World Health Organization states that demineralised waters are highly aggressive and must be stabilised, and that unstabilised soft water strongly tends to corrode metal surfaces and pipes. Distilled water also tastes flat. Remineralise it before use rather than running it neat.
- Is softened water okay for making coffee?Not ideally. Ion-exchange softening swaps each calcium and magnesium ion for two sodium ions, so hardness falls while sodium rises. The brewing standard wants sodium at or near ten milligrams per litre, and softened water typically sits well above that. It protects the machine, not the cup.
- Why does my coffee taste flat or dull?Often the water. The World Health Organization notes demineralised water tastes flat, and producers of bottled demineralised water add minerals back for taste. Water with too little dissolved mineral gives extraction nothing to work with. Check your total dissolved solids against the target of one hundred and fifty.
- What TDS should coffee brewing water be?One hundred and fifty milligrams per litre is the published target, with seventy-five to two hundred and fifty treated as acceptable. Falling anywhere inside that range meets the standard. Meters report differently depending on their conversion factor, so the same water can read as two different numbers.
Tools
Enter your own targets instead of inheriting someone else’s numbers.
- How much Epsom salt and baking soda per litre of distilled water?Dosing distilled water is pure arithmetic. Epsom salt is 9.86 percent magnesium by mass, so one litre needs 0.101 g for every 10 mg/L of magnesium you want. Baking soda is 72.6 percent bicarbonate, giving 0.067 g per litre to reach the 40 mg/L alkalinity target.