Water: the invisible ingredient

The 98% that almost no one considers

Filter coffee is approximately 98.5% water and 1.5% coffee solubles. Espresso is around 90% water and 10% solubles. Yet most people invest in machines, grinders, and origin coffee, but use tap water without thinking twice.

Water is not just a vehicle — it’s an active solvent. Its mineral composition determines how efficiently it extracts coffee compounds and how you perceive them on your palate. Changing your water can literally transform the same bag of coffee.

What’s in your water

Water contains dissolved minerals, mainly:

Calcium (Ca²⁺) and Magnesium (Mg²⁺) are the minerals that matter most to us. They’re responsible for “pulling” and extracting flavor compounds from coffee. Magnesium has particular affinity for acidic and fruity compounds. Calcium extracts more body and sweetness. The balance between them affects your cup profile.

Bicarbonate (HCO₃⁻) acts as a buffer — it neutralizes coffee acids. A little bicarbonate smooths acidity and makes it pleasant. Too much and your coffee tastes flat, opaque, lifeless. It’s like adding milk to lemon juice: the brightness disappears.

Sodium (Na⁺) in small amounts can enhance flavors (like salt in food), but in excess adds an unpleasant salty taste.

Chlorine and chloramines are disinfectants that water treatment plants add to municipal water. They produce unpleasant flavors and odors. Always filter out chlorine before brewing coffee — a basic activated carbon filter is sufficient.

The SCA standards for water

The SCA published specific standards for ideal water for coffee:

These numbers are a guide, not an absolute rule. But they give you a reference point to understand if your water is in the right range or completely off.

TDS: the quick measure

TDS (Total Dissolved Solids) of water measures the total amount of dissolved minerals, in milligrams per liter (mg/L) or parts per million (ppm) — they’re equivalent. Measured with a TDS meter that costs less than $15 USD and is the cheapest investment with the greatest impact you can make.

• Less than 75 ppm: Very soft water. Doesn’t have enough minerals to extract well. Coffee will be under-extracted, flat, flavorless.
• 75-150 ppm: The ideal range for most cases.
• 150-250 ppm: Acceptable, but can start to be “heavy.”
• More than 250 ppm: Hard water. Over-extracts, adds mineral flavors, and also destroys your equipment with scale deposits.

Distilled or pure reverse osmosis water (0 TDS) is terrible for coffee. Without minerals, water can’t extract properly — it’s like trying to clean with a dry cloth. Also, pure water is slightly corrosive and can damage espresso machine boilers.

Hard water vs. soft water

Hardness of water refers specifically to calcium and magnesium content (not total TDS, though they’re related):

Hard water (high in Ca/Mg): Extracts a lot, tends to over-extract. Produces coffee with heavy body but can be rough and opaque. Also generates scale (calcium deposits) inside boilers, pipes, and heating elements. Scale is the number one enemy of espresso machines.

Soft water (low in Ca/Mg): Extracts little. Produces thin, under-extracted, complex-lacking coffee. But it’s friendly to your equipment.

The sweet spot is water with enough minerals for good extraction, but not so much alkalinity that it crushes the acidity.

Practical options for your water

Option 1: Carbon filter (the minimum)

A Brita filter or similar removes chlorine, sediment, and some calcium. Doesn’t dramatically change mineral composition but improves basic flavor. It’s the first step and most accessible.

Option 2: Bottled water

Some bottled water brands have excellent mineral composition for coffee. The trick is checking the label and looking for waters with TDS between 75-150 ppm and moderate alkalinity. Waters like Volvic (~130 ppm) or Crystal Geyser (~100 ppm) work well, though it varies by region. In Mexico, waters like Bonafont (~200 ppm) are in the acceptable range.

Option 3: Water recipes (Third Wave Water and similar)

You start with distilled or reverse osmosis water (0 TDS) and add minerals in controlled proportions. Products like Third Wave Water sell premixed packets that you just dissolve in distilled water. You can also make your own recipes with:

• Magnesium sulfate (Epsom salts)
• Sodium bicarbonate (baking soda)

A popular basic recipe: 0.30g sodium bicarbonate + 0.75g magnesium sulfate in 1 liter of distilled water. This gives you ~100 ppm TDS with good mineral balance and alkalinity.

Option 4: Reverse osmosis system + remineralization

The most professional setup. A reverse osmosis (RO) system removes practically everything from the water, and then minerals are added back in the exact proportion. Serious specialty coffee shops use systems like BWT, Pentair Everpure, or Peak Water.

Real impact on your espresso

Water especially affects espresso because high pressure and concentration amplify any defect. Scale (calcium deposits) in the boiler reduces heating efficiency and eventually blocks pipes. Many “my machine doesn’t work well” problems are actually water problems.

If you use an espresso machine at home, descale regularly according to the manufacturer’s instructions, or better yet, use water that doesn’t generate scale in the first place.

What you need for this lesson

• A TDS meter (~$10-15 USD on Amazon or MercadoLibre) — it’s the cheapest and most revealing tool you can buy
• Your usual water (tap, filtered, bottled, whatever you use)
• Ideally, a bottle of distilled water and access to mineral bottled water to compare

Got your tools ready? Check the interactive water testing tools guide — with step-by-step instructions for the digital pH/TDS/EC meter and the API GH & KH kit, interactive calculators, and a table to record your measurements.

Practical exercise

1. Measure the TDS of your current water (tap, filtered, bottled)
2. Buy a bottle of low-mineralization bottled water (~100-130 ppm)
3. Brew the same coffee with both waters, using exactly the same recipe
4. Try them side by side and note the differences

If your tap water is above 300 ppm (common in many Mexican cities), you’ll notice a dramatic difference. If it’s between 100-200, the difference will be more subtle but real.

Key concepts from this lesson

• Your coffee is 98% water — its mineral composition matters enormously
• Calcium and magnesium extract flavor; bicarbonate neutralizes acidity
• The ideal TDS for coffee is between 75-150 ppm according to the SCA
• Very soft water under-extracts; very hard water over-extracts and damages equipment
• A $15 USD TDS meter is the best investment you can make right now
• Filtering chlorine is the minimum step; water recipes are the next level
• Hard water generates scale — the biggest enemy of espresso machines