Good brewing water is fresh drinking water without an intrusive taste, with moderate mineral content that suits the equipment. It does not need to be expensive or as pure as possible. Very hard water encourages scale. Fully demineralised water can taste flat and may be unsuitable for some machines.
Swiss tap water is generally of high quality, but hardness differs substantially by source, municipality and sometimes supply zone. Check the local water provider and the coffee-machine manual before buying filters or bottled water.
What water changes during extraction #
Water dissolves acids, aromatic compounds, products of sugar breakdown, bitter compounds and other material from the grounds. Temperature, contact time, grind size, flow and water chemistry work together. No single number explains the finished cup.
Keep these terms separate:
| Term | What it broadly describes | Why it matters |
|---|---|---|
| Total hardness | mainly dissolved calcium and magnesium | affects scale and interaction with coffee compounds |
| Alkalinity | capacity to buffer acids, often strongly influenced by bicarbonate | can soften lively acidity or make the cup dull when high |
| TDS | total amount of dissolved material | does not identify which minerals are present |
| pH | current acidity of the water | not a reliable coffee-water score on its own |
| Smell and taste | chlorine, metal, stale or other unwanted notes | transfer directly into the drink |
An inexpensive TDS meter can reveal a difference between two waters, but it does not separately measure calcium, magnesium or alkalinity. Two samples with the same TDS can behave quite differently in brewing and scale formation.
Understanding hardness in Switzerland #
The Swiss Gas and Water Industry Association explains that calcium and magnesium ions are chiefly responsible for water hardness. Switzerland commonly expresses it in French hardness degrees. 1 °fH represents 0.1 millimoles of calcium and magnesium ions per litre. The SVGW divides water into six bands, from very soft at 0 to 7 °fH to very hard above 42 °fH.
Hard water is not automatically unhealthy or unpleasant to drink. In coffee equipment, however, it creates a greater scale risk. Deposits can affect heating, flow, valves and temperature stability. Incorrect descaling can also damage an espresso machine or bean-to-cup appliance, so the manufacturer takes precedence over a generic online recipe.
The municipal figure is a starting point. A building-wide softener can change what reaches the tap. When setting up a machine, use its test-strip method where supplied and enter the correct hardness in the menu.
Temperature: a starting range, not a commandment #
For many hot filter and immersion methods, about 92 to 96°C at the coffee bed is a well-established starting range. The technical requirements for the SCA Certified Home Brewer programme use it when testing filter machines.
It is not compulsory for every coffee:
- Light roasts often need more extraction energy and may work well near the upper end.
- Very dark roasts may taste less harsh at a somewhat lower temperature.
- A pour-over, French press and espresso machine lose and deliver heat differently.
- Altitude lowers the boiling point, so water in a Swiss mountain area may boil below 100°C.
Without temperature control, bring water to the boil, allow violent bubbling to settle and pour. A universal wait of 30 or 60 seconds is inaccurate because water volume, vessel and room temperature vary. Small quantities cool particularly fast.
For a French press, hot water and about four minutes offer a practical start. For espresso at home, thermal stability and the appliance instructions matter more than an external kettle thermometer.
Tap, filtered or bottled water? #
Tap water #
The Swiss Federal Food Safety and Veterinary Office describes Swiss drinking water as generally high quality and strictly controlled. Local hardness, smell and taste remain relevant to coffee.
After water has stood in the plumbing for a long time, run the cold tap briefly until it is fresh and cool, then heat only what you need. Do not endlessly reboil a stale remainder in the kettle. Reboiled water does not suddenly become poisonous, but standing and evaporation can change taste and mineral concentration.
Activated carbon #
Activated carbon can reduce unwanted smells and flavours. It does not necessarily soften water enough on its own. Some jug cartridges combine carbon with ion exchange, while others do not. Read what the particular filter actually does.
Replace and rinse cartridges as directed. An overdue filter kept warm is not an improvement. Store filtered water cleanly and cool.
Ion exchange and machine cartridges #
Ion exchangers can replace part of the calcium and magnesium with other ions, reducing scale potential. In espresso and bean-to-cup machines, cartridges are often part of a coordinated maintenance system. Configure the machine correctly and replace the cartridge on schedule. Filtration does not automatically eliminate descaling forever.
Reverse osmosis and demineralised water #
Reverse osmosis removes much of the dissolved material. Coffee users commonly remineralise that water deliberately or blend it with other drinking water. Do not put fully demineralised water into a machine without checking. Sensors, boiler materials and manufacturer limits differ.
Bottled water #
Bottled water is useful for a comparison. Dry residue or TDS alone is not enough to choose one. Calcium, magnesium and bicarbonate influence hardness and buffering. Very mineral-rich water can create substantial scale and mute flavour; extremely low-mineral water can produce a thin cup.
Cost, transport and packaging also matter for everyday use. If local tap water works after simple filtration, bottled water is rarely the only answer.
Starting points by method #
| Method | Temperature starting point | Water issue to watch |
|---|---|---|
| Pour-over | about 92 to 96°C | taste, buffering and even flow |
| Electric filter machine | controlled by appliance | scale, cleanliness and stable heating |
| French press | about 92 to 96°C | taste and moderate mineral content |
| Espresso | commonly about 90 to 96°C, depending on machine | manufacturer limits for hardness, alkalinity and filters |
| Moka pot | determined by hob and pot | unwanted taste and scale around the valve |
| Cold brew | cold | drinking-water quality, hygiene and refrigeration |
The guides to measuring coffee and grind size show how dose and grind interact with these variables.
A useful home comparison #
Test water as you would another brewing variable:
- Make two identical coffees, one with tap water and one with filtered or suitable bottled water.
- Keep coffee, dose, grind, temperature, time and final weight the same.
- Taste both warm and again after slight cooling.
- Note sweetness, perceived acidity, bitterness, body, clarity and aftertaste.
- Over several weeks, also observe scale in the kettle or appliance.
One comparison is not a chemical analysis, but it shows whether changing water is relevant. If the cups taste the same, prioritise fresher coffee, a more consistent grinder or a more stable recipe.
Common mistakes #
Treating hardness and TDS as synonyms. Hardness mainly concerns calcium and magnesium. TDS includes all dissolved material.
Automatically choosing the softest water. The lowest possible mineral content is not necessarily best for flavour or equipment.
Overestimating a filter. Activated carbon often improves smell and taste but does not remove every form of hardness.
Ignoring the machine manual. General coffee targets can fall outside an appliance's operating or warranty conditions.
Changing water and grind together. You will not know which variable changed the cup.
Judging only by taste. Water may taste pleasant yet be hard enough to require frequent maintenance.
Key points #
Begin with fresh Swiss tap water if it tastes pleasant. Check local hardness and the equipment requirements. When taste is intrusive or scale accumulates quickly, compare a properly maintained filtration option. Use 92 to 96°C as a starting range for hot methods, not an inflexible rule.
The best choice meets three needs: a clear-tasting cup, a repeatable recipe and protection for the machine. TDS, pH or hardness alone cannot make that decision.