Water Composition and Mineral Content in Coffee Brewing

A cup of brewed coffee is roughly ninety-eight percent water. This simple fact carries a profound implication that most home brewers overlook: the character of the water you use shapes every aspect of the coffee it produces. Water is not merely a neutral solvent that carries flavor from ground to cup. It is an active participant in extraction, and its mineral composition determines which compounds it dissolves, how efficiently it dissolves them, and how the resulting flavors are perceived on the palate. Two identical coffees brewed with identical methods but different water will taste detectably — sometimes dramatically — different. Understanding water chemistry is one of the highest-leverage improvements any brewer can make, yet it remains one of the least discussed variables outside professional circles.

Why Water Chemistry Matters

Coffee extraction is a chemical process in which hot water dissolves soluble compounds from ground coffee particles. The efficiency and selectivity of this dissolution depend on the properties of the water — specifically its mineral content, pH, and alkalinity. Different minerals interact differently with the organic acids, sugars, and bitter compounds in coffee, meaning that the mineral profile of the water directly influences which flavors are extracted and how prominently they appear in the cup.

Professional baristas and competition-level brewers have understood this for years. The Specialty Coffee Association publishes water quality standards for brewing, and championship competitors routinely formulate custom water recipes optimized for specific coffees. But the principles underlying these practices are accessible to any home brewer willing to pay attention to what comes out of their tap — or what they choose to replace it with.

The Key Minerals: Calcium and Magnesium

Calcium

Calcium is one of the two primary extraction-active minerals in brewing water. It binds effectively with larger flavor molecules, including the heavy, round compounds associated with body and mouthfeel. Water with adequate calcium content tends to produce brews that feel fuller, heavier, and more texturally satisfying. Calcium also contributes to the extraction of some fruity and chocolatey notes, though its effects are less targeted than those of magnesium.

Magnesium

Magnesium is the other critical extraction mineral, and it behaves differently from calcium in important ways. Magnesium binds preferentially with the smaller, sharper organic acids and fruity compounds that contribute to brightness and aromatic complexity. Water with a higher magnesium-to-calcium ratio tends to produce brews with more pronounced acidity, more vivid fruit notes, and greater aromatic intensity. This selectivity makes magnesium particularly valuable when brewing high-quality, origin-expressive coffees where acidity and aromatics are the defining characteristics.

The balance between calcium and magnesium in brewing water is one of the primary levers available for shaping cup character. A water recipe weighted toward calcium will tend to emphasize body and sweetness. One weighted toward magnesium will tend to emphasize brightness and complexity. Neither is objectively better — the ideal balance depends on the coffee being brewed and the flavor profile the brewer is seeking.

Total Dissolved Solids and Hardness

Total dissolved solids, typically measured in parts per million, provides a general indicator of water’s mineral load. The SCA recommends a target TDS of approximately 150 parts per million for brewing, with an acceptable range between 75 and 250. Water at the low end of this range — very soft water — tends to be aggressive in extraction, pulling compounds rapidly but indiscriminately and often producing harsh, over-extracted flavors even at normal brew times. Water at the high end — very hard water — extracts more slowly and selectively but can produce flat, chalky, or muted cups if the mineral load overwhelms the delicate flavor compounds.

Hardness, which specifically measures calcium and magnesium content, is a more targeted metric than total TDS because it isolates the minerals most directly involved in flavor extraction. Water can have a relatively high TDS due to sodium or other non-extraction-active minerals while having low hardness — and this water would behave very differently in brewing than water with the same TDS composed primarily of calcium and magnesium.

Alkalinity and Buffering Capacity

Alkalinity — the water’s capacity to neutralize acids — is arguably the most overlooked and most consequential water chemistry variable in coffee brewing. Alkalinity is determined primarily by the concentration of bicarbonate ions. High-alkalinity water buffers the organic acids that coffee releases during extraction, neutralizing them before they reach the cup. The result is a brew that tastes flat, dull, and lifeless — the acidity that should provide vibrancy and structure has been chemically suppressed.

Low-alkalinity water, conversely, allows acids to express themselves fully. Combined with appropriate mineral hardness, low-alkalinity water produces brews with bright, well-defined acidity and clear flavor articulation. The SCA recommends alkalinity at or near 40 parts per million for optimal brewing. Water significantly above this threshold — common in many municipal supplies — will systematically mute the very qualities that make specialty coffee distinctive.

The interplay between water alkalinity and the temperature at which extraction occurs adds further complexity, since higher temperatures accelerate both extraction and acid neutralization. Understanding this interaction complements the principles explored in our discussion of the role of water temperature in coffee extraction.

Common Water Sources and Their Characteristics

Municipal Tap Water

Tap water varies enormously by location. Some cities supply water that falls naturally within acceptable brewing parameters. Others supply water that is excessively hard, excessively soft, heavily chlorinated, or high in alkalinity. Chlorine and chloramine, added as disinfectants, can contribute off-flavors to brewed coffee and should be removed through activated carbon filtration before brewing. Beyond chlorine removal, the suitability of tap water depends entirely on local mineral composition — which can be determined by requesting a water quality report from the municipal supplier or by testing with an inexpensive TDS meter.

Distilled and Reverse Osmosis Water

Distilled water and reverse osmosis water have had virtually all minerals removed. While this eliminates problematic compounds like chlorine and excess alkalinity, it also removes the calcium and magnesium that drive effective extraction. Brewing with pure distilled water produces flat, thin, under-extracted cups regardless of grind size or contact time — the water simply lacks the chemical tools to extract flavor efficiently. Distilled water is best used as a blank canvas to which specific minerals are added in controlled quantities.

Bottled Spring Water

Some bottled spring waters fall within acceptable brewing parameters and can produce excellent coffee with no modification. Others are too mineralized, too alkaline, or compositionally unsuitable. Reading the mineral analysis printed on the bottle — looking for calcium, magnesium, bicarbonate, and total dissolved solids — allows the informed consumer to evaluate suitability before purchasing. Several popular European mineral waters, with their moderate mineral content and low alkalinity, are widely used by home brewers seeking consistent, high-quality water without the complexity of custom formulation.

Building Custom Brewing Water

For brewers who want maximum control, custom water recipes offer the ability to tailor mineral content to specific coffees and preferences. The basic approach involves starting with distilled or reverse osmosis water and adding precise quantities of food-grade mineral concentrates — typically magnesium sulfate (Epsom salt) and calcium chloride dissolved in concentrated stock solutions. By varying the ratio and total concentration of these additions, the brewer can create water optimized for brightness, body, or balance.

Several published water recipes have gained widespread adoption in the specialty community. These recipes typically target TDS between 100 and 150 parts per million, hardness between 50 and 100, and alkalinity below 50. The precision required is modest — a digital scale accurate to 0.01 grams and basic arithmetic are sufficient — and the impact on cup quality can be transformative. The bloom phase of manual brewing, which we examined in our article on the science of blooming in manual brewing, is also influenced by water composition, since mineral content affects how rapidly and evenly water penetrates the coffee bed during initial saturation.

Practical Recommendations

For home brewers, the most impactful first step is simply knowing what is in their water. A TDS meter and a basic understanding of local water composition provide the foundation for meaningful improvement. If tap water is high in chlorine, a simple carbon filter removes it. If tap water is excessively hard or alkaline, blending it with distilled water can bring it into a more suitable range. And for those willing to invest a few minutes of preparation, custom water recipes offer a level of control that produces noticeably better results across every brewing method. Whatever approach a brewer chooses, proper storage of the coffee itself remains equally essential — a variable explored in our piece on how to store coffee beans properly to preserve freshness.

Conclusion

Water is the most abundant ingredient in coffee and one of the most powerful variables available to the brewer. Its mineral composition, alkalinity, and overall chemistry shape extraction efficiency, flavor balance, and sensory perception in ways that are measurable, reproducible, and significant. Treating water as a passive carrier of flavor — rather than an active participant in creating it — means accepting unnecessary limitations on the quality of every cup you brew. For any coffee drinker serious about improving their results, water chemistry is not an advanced topic. It is a foundational one.