ou brew the same beans at home and they taste dull, then brew them at a friend's place and they taste bright. Nothing changed but the tap.

A brewed cup is about 98 percent water, so the water is most of what you taste. Its minerals also help pull flavor out of the grounds, which is why the source matters more than people expect.

Use clean, filtered water with a moderate mineral content. Skip distilled water and very hard water. Those are the two ways water quietly ruins a cup.

Why the two extremes hurt

Very hard, high-mineral water is the first trap. The excess minerals mute aroma and can leave the cup flat or faintly chalky. Over time they also scale up the inside of your kettle. The cup tastes muffled.

Distilled or zero-mineral water is the opposite trap. With nothing dissolved in it, the water under-extracts and the cup tastes hollow and thin. Some mineral content actually helps the water grab flavor from the grounds, so stripping it all out works against you. The good range sits between the two.

The practical answer

Reach for clean, filtered water with a moderate mineral content. Filtered tap water is often all you need. A simple carbon filter removes chlorine, the off-note most tap water carries, while leaving enough minerals in place to brew well.

If your tap water is very hard or tastes off straight from the glass, a low-mineral bottled water is an easy swap. Taste the water on its own first. If it tastes clean to you, it will usually brew a clean cup.

The two extremes to avoid sit at the ends. Clean filtered water with moderate minerals is the good range in the middle.

Common questions

Can I just use tap water?
Often, yes. If your tap water tastes clean from the glass, filtered tap water brews a good cup. A simple carbon filter removes chlorine and is worth it if your tap water tastes of it.
Why not distilled water if it is the purest?
Because pure is the problem. Distilled water has no minerals, so it under-extracts and the cup tastes hollow. Some mineral content helps the water pull flavor out of the coffee.
Do I need to mix my own brewing water?
No. That is a Deep-Dive practice, not a Foundation one. Clean filtered water with a moderate mineral content is enough to brew well.

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