Brew Vero
Barista in PajamasWater: the ingredient you are not measuring
A brewed coffee is about 98% water. Change the water and you change the cup more than most equipment upgrades ever will.
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Grinders
- Conical vs flat burrs: what actually changes
- Does burr size actually matter?
- Grinder habits that quietly cost you shots
- Grind size by brew method, in microns
Beans
- Roast levels, and why they change how you grind
- Washed, natural, honey: what processing does to the cup
- How long to rest coffee, and how to store it
Espresso
Technique
People will spend two thousand on a grinder and then brew with whatever comes out of the tap. Water is the largest ingredient by an enormous margin, it is the cheapest thing to change, and it is the reason the same beans and the same recipe taste different in two cities.
Two numbers, not one
"Hard water" and "soft water" is too coarse a description to be useful. There are two properties, they do different jobs, and they move independently.
Hardness is dissolved calcium and magnesium. These minerals actively participate in extraction: they bind to flavour compounds in the coffee and carry them into solution. Water with almost no hardness extracts poorly, and the result tastes hollow and thin no matter how you brew it.
Alkalinity is mostly bicarbonate. It does not extract anything. It buffers acid, which means it neutralises the acidity the coffee brings. High alkalinity flattens a coffee, turning brightness into a dull chalky roundness. Low alkalinity leaves acidity unchecked, which reads as sharp and sometimes sour.
Hardness controls how much flavour you pull out. Alkalinity controls how much of the acidity survives to reach you.
The targets
The SCA water standard is the usual reference point. It is a guideline drawn up for a broad range of coffees rather than a law of nature, and plenty of good brewers deliberately sit outside it.
| Property | Target | Acceptable | What it does |
|---|---|---|---|
| Total dissolved solids | 150 mg/L | 75 – 250 | Overall mineral content |
| Calcium hardness | 68 mg/L | 17 – 85 | Extraction strength |
| Total alkalinity | 40 mg/L | near 40 | Acid buffering |
| pH | 7.0 | 6.5 – 7.5 | Less important than the two above |
| Sodium | 10 mg/L | near 10 | High sodium tastes flat and salty |
Diagnosing your water by taste
| The cup tastes | Likely cause | Try |
|---|---|---|
| Flat, dull, muted acidity | Alkalinity too high | Dilute with distilled water |
| Thin, hollow, watery | Hardness too low | Add minerals |
| Harsh, sharp, sour | Alkalinity too low | A pinch more bicarbonate |
| Chalky or slightly salty | Too much total mineral | Dilute |
Fixing it
If your tap water is hard, the simplest fix is dilution: cut it with distilled or deionised water until it lands in range. No chemistry required, and you can find the ratio by taste in an afternoon.
If your water is very soft, or you want repeatability, the usual approach is to start from distilled water and add a measured mineral concentrate. Several are sold for exactly this. Home recipes using Epsom salt for magnesium and baking soda for bicarbonate are well documented and cheap, though they demand accurate scales to be worth doing.
Bottled water is a lottery unless you read the label. Look for the mineral analysis, usually printed as dry residue at 180 °C. Anything in the 50–150 mg/L region is a reasonable place to start, and some widely available bottled waters are far too mineral-heavy for coffee.
Two failure modes matter here and they pull in opposite directions. Hard water forms scale, which will eventually kill a boiler, and descaling a machine with a heat exchanger is not always straightforward. But pure distilled or RO water is the wrong answer: many machines detect the water level by electrical conductivity, and water with no minerals in it will not conduct, so the machine misreads the tank. Very low-mineral water can also be aggressive toward metal over time. Aim for the middle, and check what your manufacturer requires before changing anything, because using the wrong water can void a warranty.
Brew the same coffee and recipe twice, once with your tap water and once with supermarket bottled water that has a low dry residue. If they taste noticeably different, water is worth your attention. If not, spend the effort elsewhere.