On Water

Water is 98% of your cup, and most of us treat it as an afterthought.

We agonise over origin, roast date, grind size, and bloom time — and then pull from a kitchen tap without a second thought. It is the most overlooked variable in specialty coffee, and in many cities, it is the only one worth changing.

What you are actually looking for

Specialty coffee associations (SCA, SCAA) have published target ranges for years: total dissolved solids somewhere between 75–250 mg/L, magnesium in double digits, calcium present but restrained, chlorine absent, sodium low. These are not strict rules — they are starting points that happen to produce clean, balanced extractions with a wide range of coffees.

The short version: you want some mineral content, not too much, and no chlorine.

Chlorine kills aromatics. A heavily chlorinated tap water can flatten a floral natural Ethiopian into something tasting of tepid municipalism. The fix is either a carbon filter or a simple overnight rest in an open jug, which off-gasses most of it.

Hard water — high in calcium carbonate — causes its own problem: it competes with extraction in the cup and scale in your kettle. The cup tastes chalky and short. The kettle turns into a geology project.

Very soft water, paradoxically, is also difficult. Without minerals, extraction runs hot and sour — there is nothing for the solubles to cling to during agitation. Distilled water produces flat, sharp coffee.

A simple protocol

If you are in a hard-water city and want to improve your coffee without obsessing:

1. Run your tap cold for ten seconds. Let the overnight standing water clear before you fill your kettle. Particularly relevant if you have older pipes.
2. Use a carbon filter (Brita-style) if your water is heavily chlorinated. Replace the cartridge on schedule — a saturated filter does nothing.
3. Consider a mineral-balanced water. Volvic is a commonly recommended starting point in the UK. Evian is too hard. Still water from a mountain source, softish, is usually fine.
4. Do not use a Brita if your base water is very soft. Carbon filters soften; if you are already at the bottom of the hardness range, you will make things worse.

When it genuinely matters

Honestly, water matters most when you are trying to diagnose a cup that tastes wrong despite good coffee and careful technique. If your pour-over is consistently sour with no clear grind explanation, taste your water. If your espresso is scaling up your machine fast, test for hardness.

For most filter coffee made with decent tap water, you are probably fine. Spend the time you would have spent obsessing over mineralogy on dialling in your grinder instead.

But do run the tap cold first. It is the easiest thing you can do, and it costs nothing.