When it comes to brewing a great cup of coffee, most people focus on the beans, grind size, and brew method. But there's one ingredient that often gets overlooked—despite making up 98% of your cup: water.
The chemistry of your water can dramatically change the flavour of your coffee. Everything from the level of hardness to the pH balance and mineral content can affect how flavours are extracted—altering sweetness, acidity, body, and bitterness.
In this article, we explain how water chemistry affects coffee brewing, the role minerals play, and how using the right filters—like the Brita, Claris, or iX Water Filters—can help you brew a better cup every time.
1. Why Water Chemistry Matters in Coffee Brewing
Water isn’t just a neutral carrier—it actively extracts flavour compounds from your coffee grounds. Depending on its composition, it can either highlight or mute different flavour notes.
- Hard water (high in calcium and magnesium) can enhance body but also risk over-extracting bitterness.
- Soft water (low in minerals) often leads to under-extracted coffee that tastes flat or weak.
- Alkalinity affects how we perceive acidity and sweetness, balancing or dulling flavours.
Studies have shown that changing the mineral content of your water—even when using the same beans and brew method—can produce dramatically different results (Hendon et al., 2014).
2. How pH Levels Shape Coffee Flavour
pH measures how acidic or alkaline your water is, on a scale from 0 to 14. Neutral water sits at 7.
- The ideal brewing range is around pH 6.5 to 7.0, as recommended by the Specialty Coffee Association (SCA).
- If your water is too acidic (below pH 6.5), your coffee may taste sour or overly sharp.
- If it’s too alkaline (above pH 7.5), acidity is suppressed, resulting in a dull, lifeless cup.
While pH doesn’t directly change flavour, it affects how minerals interact with acids and oils during extraction (Clarke & Macrae, 1988).
3. Hardness: The Role of Calcium and Magnesium
Water hardness refers to the concentration of minerals—mainly calcium and magnesium. These minerals affect how much flavour is extracted and which notes are emphasised.
a. Calcium (Ca²⁺)
- Adds body and boosts sweetness by helping extract certain compounds.
- Too much calcium (over 100 mg/L) can lead to bitter or astringent coffee.
- It also contributes to limescale build-up in espresso machines.
b. Magnesium (Mg²⁺)
- Often delivers more vibrant and fruity flavours than calcium.
- Enhances the solubility of acids, bringing out complexity and brightness.
- Levels over 30 mg/L can make coffee overly sharp or acidic.
SCA Recommended Total Hardness: 50–175 ppm
Sweet spot for most brews: 80–120 ppm
4. Alkalinity: Balancing Acidity and Bitterness
Alkalinity is the measure of bicarbonates (HCO₃⁻) in your water. These act as buffers, controlling how much acidity is perceived in the final cup.
- Low alkalinity (<40 mg/L): Can result in sour, overly acidic coffee.
- High alkalinity (>100 mg/L): Mutes acidity, making coffee taste flat or chalky.
The ideal range is 40–80 mg/L, giving you a bright cup with balanced acidity and sweetness.
5. Sodium and Potassium: The Minor Players
While less discussed, sodium and potassium can subtly influence flavour.
- Sodium (Na⁺) at low levels (under 10 mg/L) can enhance sweetness. Above 30 mg/L, it may taste salty.
- Potassium (K⁺) can also bring out sweetness but is usually present in only trace amounts in tap water.
6. The Best Water for Brewing Coffee
a. SCA Recommended Water Standards
| Parameter | Ideal Range |
|---|---|
| pH | 6.5 – 7.5 |
| Total Hardness | 50 – 175 ppm |
| Calcium | 17 – 85 mg/L |
| Magnesium | 10 – 30 mg/L |
| Alkalinity | 40 – 80 mg/L |
| Sodium | <10 mg/L |
b. Real-World Application: How Cafés Optimise Water
Many specialty cafés use reverse osmosis (RO) systems to strip water of all minerals and then remineralise it with precise ratios.
7. How to Test and Improve Your Water
Test Your Water:
- TDS meters measure total dissolved solids (in ppm).
- Hardness kits and pH strips are available from aquarium or coffee suppliers.
Improve Your Water:
- Carbon filters (e.g., Brita) reduce chlorine and some organic matter.
- Reverse osmosis systems remove all minerals—ideal if you plan to add them back manually.
- Remineralisation: Add calcium or magnesium salts in small amounts to customise flavour extraction.
8. How Water Filters Help Make Better Coffee
Water filters are important for controlling mineral levels and removing unwanted tastes like chlorine. They also protect your coffee equipment from scale buildup, which can shorten machine life and affect flavour.
We offer commercial water filters that are perfect for coffee setups:
- Brita Purity C: Designed for busy cafés and coffee machines, it reduces limescale and chlorine but keeps important minerals like calcium and magnesium balanced.
- Claris Ultra: Made for espresso machines, it controls hardness and alkalinity to protect your machine and ensure consistent flavour.
- iX 01/02 Water Filters: These are great for commercial and catering setups, offering reliable scale protection and excellent water quality for the best coffee results.
Using these filters helps bring your water closer to the ideal standards, so your coffee tastes just right every time.
9. What the Science Says
- Hendon et al. (2014) – Magnesium extracts flavour compounds more effectively than calcium.
- Clarke & Macrae (1988) – Water pH influences acidity perception in brewed coffee.
- Illing et al. (1997) – Bicarbonates play a major role in balancing sharpness and smoothness.
Water chemistry is one of the most important—and underrated—factors in coffee brewing. The right balance of minerals can bring out clarity, sweetness, brightness, and body, while the wrong water can make even the best beans taste flat or harsh.
If you're serious about getting the most out of your coffee, testing and adjusting your water could be one of the easiest and most impactful changes you make.