Water for brewing coffee
A cup of coffee is about 98% water, and its minerals change how the coffee tastes. What hardness and alkalinity do, what to aim for, and simple ways to get good brewing water from the tap, a bottle or mineral packets.
Why water matters
Brewed coffee is about 98% water, so the water you start with is most of what you drink. It isn't just a carrier, either: the minerals dissolved in it help pull flavor out of the grounds, and some of them change how the finished cup tastes.
That's why the same bag can taste bright and sweet at a café and flat or harsh at home, even with the same recipe. If a coffee never tastes like the roaster's notes and you've already worked through ratio, grind and time, the water is the next thing to look at.
Water matters most for light roasts. Their bright, fruity acidity is exactly what the wrong water flattens. Darker roasts are more forgiving.
What's in it, and what each part does
- Hardness
- Calcium and magnesium. They help extract flavor, so some hardness is good: very soft water tends to brew thin, hollow coffee. Too much leaves scale in kettles and machines, and can taste chalky.
- Alkalinity
- Mostly bicarbonate, the part people overlook. It neutralizes acid, so a little keeps coffee from tasting sharp, but too much cancels the acidity that makes a light roast taste of fruit and leaves it flat and dull. High alkalinity is the most common reason good coffee tastes muted at home.
- Chlorine and chloramine
- Cities add them to keep tap water safe, and both give coffee a medicinal or swimming-pool note. A carbon filter (a pitcher or fridge filter) removes chlorine well; chloramine needs a filter rated for it.
- Sodium
- A little doesn't matter. Water from a home water softener is the problem: the softener swaps calcium and magnesium for sodium and leaves the alkalinity, the worst of both.
- TDS
- Total dissolved solids, everything dissolved in the water, in parts per million (ppm). A cheap TDS meter tells you how much is there but not what it is, so two waters with the same reading can brew very differently.
What to aim for
The Specialty Coffee Association publishes a water standard for brewing. You don't need to hit it exactly; it's a target range that tells you whether your water is close or far off.
A simpler rule of thumb: hardness should be higher than alkalinity, so there's enough calcium and magnesium to extract with and not so much bicarbonate that it cancels the coffee's acidity. Many brewers also find that magnesium brings out brighter, fruitier notes and calcium rounder, heavier ones, which is why water for light roasts often leans on magnesium.
| What | Target | Acceptable range |
|---|---|---|
| Total dissolved solids | 150 ppm | 75 to 250 ppm |
| Calcium hardness | 68 ppm | 17 to 85 ppm |
| Alkalinity | 40 ppm | At or near 40 ppm |
| pH | 7.0 | 6.5 to 7.5 |
| Sodium | 10 ppm | At or near 10 ppm |
| Chlorine | None | None |
Hardness and alkalinity are given as ppm of calcium carbonate, the way water reports and test strips usually show them. Many specialty roasters and competition baristas brew with softer water than this, especially for light roasts.
Finding out what's in your tap
Your water utility publishes an annual water quality report (search for your city's name and "water quality report"). It lists hardness, and often alkalinity and pH. Hard water is common across much of the Southwest, Texas, Florida and the Midwest; a reading over about 150 ppm hardness, or alkalinity well over 40 ppm, will hold coffee back.
For your own glass, aquarium test strips for GH (hardness) and KH (alkalinity) are cheap and close enough. If you're on a well or a water softener, test rather than relying on the city's report.
Your options, from easiest
- Filtered tap water
- If your tap is moderate (roughly 50 to 150 ppm hardness and alkalinity not far over 40), a carbon pitcher filter is all you need: it takes out chlorine and off flavors. It won't fix hard water; pitcher filters remove little hardness and almost no alkalinity.
- Hard tap water cut with distilled
- If your tap is hard, mixing it with distilled water brings the hardness and alkalinity down together, for much less than buying all your water. Half and half halves both; use your water report to pick the mix that lands near the targets above, run the tap through a carbon filter first, then adjust by taste.
- Bottled spring water
- Look for a still spring water whose label or website lists low total dissolved solids (about 50 to 150 ppm) and low bicarbonate. Skip mineral waters, which are far too hard, and "alkaline" waters, which are made to have exactly what you don't want. Brands vary by source, so check the analysis rather than the name.
- Distilled water plus minerals
- The most consistent option and what many home brewers end up using: a gallon of distilled or reverse-osmosis water with a packet or a few drops of coffee minerals added (Third Wave Water, Lotus, Apax Lab and others). You get the same water every time, wherever you are. Plenty of light-roast brewers use packets at half strength or less, a packet to two gallons, which makes softer water and halves the cost; try both and taste.
- What to avoid
- Fully demineralized distilled or reverse-osmosis water on its own (nothing to extract with, so the coffee tastes hollow and sour), water from a home softener, alkaline water, and anything that smells of chlorine. Reverse-osmosis water that still has some minerals in it, around 50 ppm, isn't in this list: it can brew very well, so taste it before replacing it.
A quick taste test
Brew the same coffee twice, side by side, with the same recipe: once with your usual water and once with distilled water plus a mineral packet, or a low-mineral spring water. Taste them as they cool.
If the second cup is noticeably brighter, sweeter or clearer, your water has been holding your coffee back, and changing it will do more than a new grinder. If you can't tell them apart, your tap is fine and you can stop worrying about it.
Kettles and espresso machines
Hard water leaves scale in kettles and espresso machines over time. Descale a kettle with citric acid when you see white buildup; for an espresso machine, follow the maker's water guidance, since scale is a common cause of repairs and some warranties exclude it.
Don't run an espresso machine on pure distilled water unless the maker says to: some machines use the minerals in water to sense how full the tank or boiler is. Distilled water with coffee minerals added is fine.