Water for coffee
A cup of filter coffee is about 98% water, and the minerals in it decide how much flavour comes out of the grounds. Water that’s too hard tastes flat and chalky and scales your kettle; water with almost nothing in it (distilled, reverse osmosis) tastes sour and thin. Most people get a big improvement just by filtering their tap water.
What to aim for
The Specialty Coffee Association’s standard for brewing water.
| Measure | Target | Range |
|---|---|---|
| Total dissolved solids | 150 mg/L | 75–250 mg/L |
| Calcium hardness | 68 mg/L | 17–85 mg/L |
| Total alkalinity | 40 mg/L | at or near 40 mg/L |
| pH | 7.0 | 6.5–7.5 |
| Sodium | 10 mg/L | at or near 10 mg/L |
| Chlorine | 0 | none |
Hardness and alkalinity are given as mg/L of calcium carbonate, the same as ppm. A cheap TDS pen gives you the first number; aquarium test strips (GH and KH) give you the next two.
Pick your water
- Filtered tap (the easy win). A carbon pitcher or tap filter removes chlorine and off tastes. If your tap water is moderately soft, that may be all you need.
- Hard tap water (white scale in the kettle, flat or chalky coffee). Use a filter that softens as well as cleans (ion-exchange cartridges), or mix your tap water half and half with distilled water.
- Bottled. Choose a low-mineral spring water and check the label: total dissolved solids around 75–150 mg/L and not much sodium. Avoid mineral waters with high TDS.
- Mineral packets. Sachets made for coffee that you add to distilled water. Easiest way to get repeatable water without measuring.
- Make your own. Distilled water plus two simple concentrates (below). Cheapest and most repeatable, and you can try different recipes.
Make your own: two concentrates
Make each in a clean bottle with distilled (or reverse osmosis) water, label it, and keep it in the fridge. Use food-grade ingredients from the grocery store or pharmacy.
- Buffer: 1.68 g baking soda (sodium bicarbonate, not baking powder) in 1 L of distilled water. This sets alkalinity (KH), which softens acidity.
- Hardness: 2.45 g Epsom salt (magnesium sulfate, unscented) in 1 L of distilled water. This sets hardness (GH), which pulls flavour from the coffee.
Each concentrate is about 1000 ppm, so 1 g of it in 1 L of finished water adds about 1 ppm.
Mix a batch
Middle of the SCA standard. A balanced place to start.
Weigh the concentrates into a jug, then top up with distilled water to the total. Start with the SCA target; if your coffee tastes sharp, try Rao; if it tastes flat, try less buffer or more hardness.
Espresso machines
These recipes are for kettle brewing. Espresso machines have their own needs: hard water builds scale in the boiler, and very soft or chloride-rich water can corrode it. Check your machine maker’s water advice and warranty before using home-made water in it.
Recipes from Barista Hustle’s “DIY Water Recipes Redux” (2019). Targets from the SCA’s water standard. See also Home cupping to taste two waters side by side.