What Water to Use for Coffee
Your cup is about 98% water. It's also the last thing most people check, long after they've bought the grinder, the scale and the gooseneck kettle.
Water is the variable most often described as transformative. It's also the one most likely to send you down an expensive hole. Here's what it's worth, and what it costs.
The short answer is your tap
An r/pourover thread asked what everyone actually uses for brew water. The most-upvoted answer, in a sub full of people who mix their own minerals, was tap water.
Several regulars said the same thing plainly. Their tap tastes fine, so their coffee tastes fine. Start there and make it prove it isn't good enough.
Measure yours before you buy anything
You can't work out your water from your city's name. A thread about flat pour overs went sideways over exactly this. One commenter cited a municipal hardness report to argue the poster's water was hard.
They were reading the report for the wrong city. Both people were reasoning honestly from real documents, and they reached opposite conclusions, because a city name is not a water spec.
The fix came from the same thread. A meter that reads total dissolved solids is about $20.
The ladder, and what each rung costs
This is the community pricing the rabbit hole out loud, rung by rung. Climb it until the coffee stops improving, then stop.
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Tap, or tap through a filter pitcher
Free, or the cost of a filter
Several regulars in the thread say their tap tastes fine, so their coffee tastes fine. One puts it at 90% of the way there. This is where most people should stop.
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Filter pitcher plus mineral drops
Around $1 per treated gallon
A ZeroWater pitcher strips the water, then mineral drops put back what you want. Reported as the easiest custom setup, and the drops last months.
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Distilled plus a mineral sachet
Bottled water plus sachets
Third Wave Water is the common one. The sub tends to run it at half strength rather than full. Its weakness is supply. This rung breaks when your shop stops stocking distilled.
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Under-sink reverse osmosis
Roughly $30 for a pre-filter, $50 for a membrane
The convenience endgame. One member reports total dissolved solids falling from 200–350 down to 8. Carbon filters every 6–12 months, membrane every 3–5 years.
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Mixing your own concentrate
Cheapest per gallon, most effort
Potassium bicarbonate, calcium chloride and magnesium sulfate, mixed into distilled water. The cheapest rung per gallon and where the experienced users end up.
The quantities people use for their own mixes contradict each other, so none of them are written here as a recipe. If you get to that rung, you'll want to read the people who mix daily rather than a chart.
The numbers, if you want them
The SCA's targets are 50 to 175 ppm total hardness and 40 to 75 ppm carbonate hardness. Those are recommendations rather than a recipe, and the right end of the range depends on what you're brewing.
| If you're brewing | Lean |
|---|---|
| Filter coffee | Softer, around 100 ppm |
| Espresso | Harder and more alkaline |
| Dark roasts | Softer |
| Light, bright roasts | Harder |
Above about 550 ppm, reverse osmosis is the practical answer. Below that, a carbon stick in soft-water areas or an ion-exchange filter in hard-water areas will move you toward the range.
One more, and it costs nothing. A pinch of baking soda mellows a coffee that reads too bright or too sour.
Blind-test it before you commit
The most useful post in that same thread came from someone who bought the minerals, mixed their own concentrates, and ran blind tastings across several concentrations against both distilled and tap.
Tap performed well in all of them, so they stopped. Their advice was not to start from distilled at all, and to blind-test anything you're thinking of buying.
That's the honest shape of this whole subject. Water can change your cup. It's also the easiest place in home coffee to spend money on a difference you can't taste.
When water isn't the problem
If the cup is sour, bitter or flat, water is near the bottom of the list of suspects. Grind, temperature and contact time move the cup much further.
Work through the brewing diagnostic first, and check your ratio second. Come back here when those two are right and something still isn't.
One more variable, every Thursday
Coffee Enthused Weekly is technique you can test tomorrow morning, origins and gear. About ten things worth knowing, every Thursday. Free.