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Water is most of every coffee drink, but espresso contains a much higher concentration of coffee solids than filter coffee. Water chemistry affects flavour as well as scale, corrosion and sensor operation. For espresso machines, start with the manufacturer’s water specification.
Water TDS describes the concentration of dissolved material, usually in mg/L or ppm. A pocket conductivity meter estimates TDS; it cannot identify the minerals present or measure hardness and alkalinity separately. The same TDS value can describe waters with very different effects. Do not use it alone to approve water for your machine.
Calcium and magnesium contribute to hardness and influence extraction. Their effects depend on the full water composition. Follow your machine’s permitted hardness range. When comparing specifications, check whether a value refers to the element itself or an equivalent concentration expressed as CaCO3.
Alkalinity describes water’s acid-buffering capacity; it is not the same as pH or total hardness. Higher alkalinity can reduce perceived coffee acidity. Reported bicarbonate and alkalinity as CaCO3 use different units and should not be compared directly. Filter-coffee targets are not automatically suitable espresso-machine specifications.
Do not assume distilled or reverse-osmosis water is suitable for an espresso machine without treatment. Very low mineral content can affect water-level detection and corrosion risk in some models. It does not universally cause over-extraction. Use water within the manufacturer’s limits; remineralise an RO base only with a compatible, measured recipe.
Obtain a water report or test hardness and alkalinity as your machine maker recommends. Choose a compatible filter or a known bottled-water composition and retest after treatment. Carbon filtration may remove chlorine without substantially reducing hardness. Avoid arbitrary blends: their final chemistry depends on both starting waters.
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