How Water Quality Affects the Taste of Tea and Coffee

Why Water Is the Most Overlooked Brewing Variable

Coffee is approximately 98% water. Tea is even closer to 99%. Despite this, water chemistry is often the last variable home brewers consider when a cup tastes off. Before adjusting grind size, steep time, or leaf grade, it is worth understanding what the water itself is doing to your brew.

Water acts as a solvent, pulling aromatic compounds, acids, oils, and other flavor-active molecules out of coffee grounds and tea leaves. The efficiency and selectivity of that extraction process depends heavily on the dissolved minerals present — or absent — in the water. Bitterness, for example is often attributed to over-extraction or roast level, but water chemistry plays a contributing role that is frequently overlooked.

Key Minerals and What They Do

Not all minerals behave the same way in a brew. The two most important for extraction are magnesium and calcium.

• Magnesium is particularly effective at binding to flavor compounds in both coffee and tea, enhancing perceived sweetness and complexity. Research in sensory science consistently shows that magnesium-rich water increases the intensity of desirable flavors.
• Calcium also aids extraction but in a less targeted way, contributing to body and mouthfeel more than flavor nuance.
• Bicarbonate acts as a buffer that neutralizes acids. High bicarbonate levels flatten acidity in coffee and can make tea taste dull and chalky — a common complaint in areas with very hard water.
• Sodium in low concentrations can enhance sweetness, but elevated levels introduce saltiness that overwhelms delicate flavors.
• Chlorine and chloramines, common in municipal tap water as disinfectants, bind to aromatic compounds and suppress the floral and fruity notes that make specialty teas and single-origin coffees distinctive.

Understanding this mineral interplay helps explain why the same beans brewed in two different cities can produce noticeably different cups. Processing methods shape a coffee's potential flavor, but water determines how much of that potential actually reaches your palate.

Hardness, Softness, and the Brewing Sweet Spot

Water hardness is a measure of the total concentration of calcium and magnesium ions, usually expressed in parts per million (ppm) or grains per gallon. Both extremes — very soft and very hard — create problems.

Very soft water (under roughly 50 ppm TDS) lacks the mineral scaffolding needed for good extraction. Brews tend to taste sour, thin, or unbalanced, as acids are extracted unevenly without adequate buffering.

Very hard water (above roughly 300 ppm TDS, particularly when high in bicarbonate) over-buffers the brew, suppressing acidity and brightness. Tea brewed in such water frequently tastes flat or metallic, while coffee can taste chalky or muted.

The Specialty Coffee Association has published water quality guidelines that most specialty brewers use as a reference point: a target TDS of around 150 ppm, with bicarbonate levels ideally kept moderate to preserve acidity. Similar principles apply to tea, particularly for more delicate varieties like green and white teas. The differences between green, oolong, and black teas mean that each may respond slightly differently to water chemistry.

pH, Temperature, and Practical Considerations

Water pH — the measure of acidity or alkalinity on a scale from 0 to 14 — also shapes the final cup. Slightly acidic water (pH 6.5–7.5) is generally considered ideal for coffee brewing. Water that is too alkaline tends to dull the bright, fruity notes prized in lighter roasts. For tea, similar principles apply, though robust black teas are more tolerant of moderate alkalinity than green or white varieties.

Temperature interacts with water chemistry as well. Hotter water extracts more aggressively, which in hard water can amplify the chalky or bitter notes that bicarbonate produces. This is one reason why cold-brew coffee made with hard tap water sometimes tastes smoother — slower, cooler extraction is less affected by bicarbonate interference.

For most home brewers, a straightforward activated carbon filter is the most accessible intervention. These filters effectively remove chlorine and chloramines without stripping beneficial minerals, making them a practical first step. Those seeking more precision can explore pitcher filters with remineralization stages or look into commercially formulated brewing water options. The broader relationship between water and dietary health is a separate consideration, but filtered water often serves both brewing and hydration goals simultaneously.