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TroubleshootingUpdated 23 August 2026

The Science of Water for Coffee

Your coffee is 98% water. Why filtered tap water often isn't enough, and how to build the perfect brewing water.

Coffee is roughly 98.5% water (and espresso is about 90% water). It stands to reason that if your water tastes bad, your coffee will taste bad.

But it goes deeper than that. Water isn't just a solvent; it's an active participant in the chemical reaction of brewing. The minerals in your water literally grab onto the flavor compounds in the coffee bean.

Why Tap Water is Unpredictable

Tap water varies wildly from city to city.

  • If your water is too hard (lots of calcium and magnesium), it will over-extract the coffee, making it muddy and dull (and it will destroy your espresso machine with scale).
  • If your water is too soft (like distilled or reverse osmosis water), it lacks the minerals needed to grab the flavor compounds, resulting in flat, hollow, and highly acidic coffee.
  • If your water has chlorine, it will immediately impart a chemical taste to the brew.

The Three Pillars of Coffee Water

To brew the best coffee, you need to manage three things:

  1. Zero Chlorine/Chloramine: Use a carbon filter (like a Brita) to remove these immediately.
  2. General Hardness (GH): This is the measure of Calcium and Magnesium. These minerals act as the "flavor extractors." You need some of them, but not too much.
  3. Carbonate Hardness (KH / Alkalinity): Think of this as a buffer. It neutralizes the natural acids in the coffee. High alkalinity will mute all the bright, fruity flavors. Low alkalinity will result in a sharp, sour cup.

How to Get the Best Water

1. The Easy Way: Bottled Spring Water Many people simply buy bottled spring water. However, you have to check the label. You are looking for a TDS (Total Dissolved Solids) of around 100-150 mg/L.

2. The Nerd Way: Remineralization The most consistent way to get perfect water is to start with completely empty water (Distilled or Reverse Osmosis) and add the minerals back in yourself.

You can do this by:

  • Buying packets of pre-mixed minerals (like Third Wave Water) and dumping them into a gallon of distilled water.
  • Making your own mineral concentrates using Epsom Salt (Magnesium) and Baking Soda (Alkalinity) using recipes found online (search for "Barista Hustle Water Recipes").

By controlling your water, you eliminate the biggest invisible variable in coffee brewing.