Why Water Quality Matters in Pour-Over Coffee (Alkalinity, Hardness & Flavor Explained)

 The coffee we drink is, at its core, water that has dissolved the flavorful compounds inside coffee grounds. In fact, more than 98% of a cup of pour-over coffee is water.

We spend so much time chasing the best origins and growing regions, the most suitable processing methods, the perfect roast profiles, and the most precise brewing techniques—yet all of these efforts ultimately rely on water to carry the coffee’s flavor. If we overlook the foundational role of water, everything else can easily fall apart.

**No.1

Water Plays Two Core Roles in Coffee Brewing: Extraction and Flavor**

Water is responsible for extracting soluble flavor compounds from coffee grounds, and it also makes up the body of the final beverage itself. The chemical composition of the water directly influences what ends up in your cup.

**No.2

The Soluble Compounds in Water: Alkalinity and Hardness**

Water contains both negatively charged ions and positively charged ions.

  • The concentration of negatively charged ions determines total alkalinity

  • The concentration of positively charged ions determines total hardness

1. Total Alkalinity — Mainly Bicarbonate Ions

Bicarbonate ions act as a buffer in brewing water, helping neutralize acidity and keep the pH within a suitable range. The higher the bicarbonate content, the higher the alkalinity, and the stronger its ability to suppress acidic compounds in coffee.

When alkalinity is too high, it can neutralize or even mask coffee’s pleasant natural acidity, making the cup taste dull, flat, or even slightly “soda-like,” while amplifying bitterness and reducing clarity.
When alkalinity is too low, buffering capacity weakens, causing acidity to become sharp, aggressive, and lacking roundness.

2. Total Hardness — Calcium and Magnesium Ions

Calcium and magnesium ions are highly effective at binding to coffee’s flavor compounds—especially desirable acids, sweetness, and oils. Without them, extraction efficiency drops significantly.

Magnesium is particularly good at extracting floral and fruity aromas, while calcium contributes more to body and mouthfeel. This is why some high-end brewing waters carefully adjust the calcium-to-magnesium ratio.

If hardness is too high (>150 ppm as CaCO₃), coffee tends to extract excessive bitterness and astringency, loses vibrancy, and forms scale on equipment.
If hardness is too low (<50 ppm as CaCO₃), the coffee tastes hollow, thin, overly acidic, and lacking sweetness and body.

According to the Specialty Coffee Association (SCA), recommended ranges are:

  • Alkalinity: 40–75 ppm

  • Total hardness: 50–175 ppm

**No.3

pH: Another Critical Water Parameter**

The SCA recommends a brewing water pH between 6.5 and 7.5, with an ideal target around 7.0.

pH measures acidity and alkalinity. Brewing coffee with alkaline water (pH above 7) reduces perceived acidity—the higher the pH, the stronger the buffering effect. Simply put:

  • Higher pH → lower perceived acidity

  • Lower pH → higher perceived acidity

However, higher alkalinity is not always better. Excessively alkaline water often leads to bitterness and astringency, dulling the coffee’s character.

**No.4

How to Create Better Brewing Water**

1. Test Your Water

Use a TDS meter or a dedicated water testing kit to understand your current brewing water.

2. Choose a Solution

(1) Basic Option: Filtered Water
Activated carbon filters remove chlorine, odors, and organic compounds, improving taste. While they have limited effect on hardness, they’re a solid starting point for most homes and cafés.

(2) Intermediate Option: Bottled Water Blending
Mixing low-mineral purified water with mineral water at specific ratios is an affordable and effective way to improve brewing water.

(3) Professional Option: Custom Brewing Water
Using third-party mineral packets or an RO (reverse osmosis) system with remineralization filters allows precise control. Many competition brewers use this approach to tailor water for specific coffees.

Water quality is one of the most underestimated variables in pour-over coffee. When we care about origin, processing, roast profiles, and brewing techniques, we should also care about the water we use—because that’s often the final key to unlocking a truly exceptional cup.

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