Great brewing water is a spec, not a brand. With a jug of distilled water, plain Epsom salt, baking soda, and an ordinary 0.1 g coffee scale, you can build water to the SCA's published targets for pennies a liter, then tune it for light roasts or a scale-wary espresso machine.
Why Build Your Own Water?
Water is not a passive carrier. The dissolved magnesium and calcium in it do much of the actual extracting, binding to flavor compounds and pulling them out of the grounds, while bicarbonate acts as a chemical shock absorber that neutralizes acids as they arrive in the cup.
Those are the two numbers that matter. Hardness is the total dissolved magnesium and calcium, the extraction engine: too little and coffee tastes hollow and thin, too much and it turns heavy and dull. Alkalinity is the bicarbonate buffer: too little and acidity lands sharp and unpadded, too much and it flattens a bright coffee into cardboard. Both are measured in ppm "as CaCO3" so they share one scale. That is the theory in a paragraph; the full version, including what your tap is probably doing wrong, lives in our water quality guide.
Why build instead of filter or buy? Repeatability. Tap water drifts with the seasons and carries chlorine, and bottled water is a lottery. Starting from distilled water and adding exactly what you want is the only approach where Tuesday's brew water matches Monday's. The book Water for Coffee, by barista champion Maxwell Colonna-Dashwood and chemist Christopher Hendon, is what put this practice, and magnesium in particular, on the specialty map.
What Does the SCA Standard Say?
The Specialty Coffee Association publishes target ranges for brewing water:
- Total dissolved solids: 75 to 250 ppm, target 150
- Calcium hardness: 17 to 85 ppm as CaCO3, target 68
- Total alkalinity: at or near 40 ppm as CaCO3
- pH: 6.5 to 7.5, target 7
- Chlorine: none
The recipes below use magnesium instead of calcium. It extracts at least as well, it doses cleanly from a supermarket ingredient, and it sidesteps most limescale, which is calcium carbonate.
Make the Two Stock Concentrates First
Hitting 40 ppm of alkalinity in one liter takes about 0.07 g of baking soda. No kitchen scale can weigh that. Concentrates solve the precision problem: weigh a large amount once, then dose the solution by the gram.
- Hardness concentrate: dissolve 24.6 g of plain Epsom salt (unscented USP magnesium sulfate, nothing added) in 1,000 g of distilled water and shake until clear. Each gram of this concentrate added to a liter of water contributes roughly 10 ppm of hardness as CaCO3.
- Buffer concentrate: dissolve 16.8 g of baking soda in 1,000 g of distilled water. Each gram added to a liter contributes roughly 10 ppm of alkalinity as CaCO3.
Label both bottles clearly, because they look identical, and store them capped at room temperature. Nothing in them spoils, and a batch lasts months. This is the same stock-solution logic behind Barista Hustle's published water recipes, scaled here so a 0.1 g coffee scale is all the precision you need.
The Three Recipes
Mixing a batch takes two minutes:
- Set a clean, empty 1 liter bottle on the scale and tare.
- Add the concentrate weights from the table below.
- Fill with distilled water to 1,000 g total, cap, and shake.
The water mixing calculator is the interactive companion to this guide: give it a custom hardness and alkalinity target, or an odd batch size, and it does the arithmetic for these exact concentrates.
| Recipe | Hardness (ppm as CaCO3) | Alkalinity (ppm as CaCO3) | Hardness concentrate | Buffer concentrate |
|---|---|---|---|---|
| Everyday balanced | About 80 | About 40 | 8 g per liter | 4 g per liter |
| Light roast clarity | About 100 | About 25 | 10 g per liter | 2.5 g per liter |
| Espresso low-scale | About 50 | About 25 | 5 g per liter | 2.5 g per liter |
Everyday balanced lands close to the SCA targets, with total dissolved solids right around the 150 ppm mark. If you make one water, make this one. It flatters every brew method and every roast level.
Light roast clarity raises extraction power and cuts the buffer so delicate acidity reads clearly instead of being neutralized. It deliberately pushes hardness past the SCA window; clarity waters usually do. If cups turn sharp, add buffer concentrate 0.5 g at a time, and rule out the usual technique suspects with our sour and bitter troubleshooting guide first.
Espresso low-scale keeps total minerals modest for machines while leaving enough buffer to protect the boiler and the flavor. Low scale, note, not no scale.
The Machine Scale Warning
Limescale is mostly calcium carbonate, and these recipes contain no calcium, which removes the main threat. Magnesium can still deposit slowly in a hot boiler when alkalinity runs high, which is why the espresso recipe keeps the buffer low. Two more cautions. Check your machine's warranty language before switching water, since some manufacturers specify mineral ranges. And do not run straight distilled water instead: it brews hollow, and some machines sense water level with conductivity probes that cannot detect near-pure water. Whatever you run, stay on a normal descaling schedule. Cheap insurance beats a dead boiler.
What About Store-Bought Water?
Bottled water can approximate these recipes if you read the mineral analysis instead of the marketing. Look for total minerals (listed as dry residue or TDS) between 50 and 150 ppm, bicarbonate under about 75 mg/L, and low sodium. Skip two categories: "purified" reverse-osmosis water, which is nearly empty and brews flat and sour, and heavily mineralized waters, whose bicarbonate flattens coffee and feeds scale. The commercial mineral packets sold for coffee do the same job as our concentrates at many times the price per liter.
The Bottom Line
Mix the everyday recipe, brew your usual coffee side by side against tap, and taste. For most people the difference is immediately obvious, especially on light roasts, and the ongoing cost is a jug of distilled water and a few grams of pantry minerals. If your tap already tastes clean and your kettle never scales, you may be one of the lucky ones and can skip the whole exercise. Everyone else should remember that water sets the ceiling on a brew; grind and brew temperature still decide whether you reach it.