Water changes both flavour and machine health
Minerals help coffee extraction, but scale-forming hardness can build up inside heaters and water paths. Very low-mineral water can also taste flat and may fall outside a manufacturer’s instructions. The practical target is not simply the lowest possible number; it is water that tastes suitable and remains within the guidance for the exact machine.
Do not treat TDS as a hardness measurement
A handheld TDS meter estimates the total dissolved material that conducts electricity. It does not identify which minerals are present and cannot, by itself, tell you how much scale the water will form. Use a hardness test or a local-water report where appropriate, then follow the machine maker’s setup process.
Start with the manual, not a universal recipe
Machines differ in boiler materials, filter systems, hardness settings and descaling programmes. Some ask the owner to test water and select a hardness level; some detect a proprietary filter; others use a simple timed routine. Instructions for a similar-looking sibling are not automatically safe for your exact model.
A tank filter is not a permanent exemption from scale
Manufacturer filters can reduce hardness or other compounds under specified conditions, but their capacity is finite. Replacement timing may depend on elapsed time, water volume or the machine’s setting. If either the compatible filter or cadence is unknown, keep that gap visible rather than promising a fixed annual cost.
Softened and bottled water need checking too
Domestic ion-exchange softeners may replace calcium and magnesium with sodium, while bottled waters vary widely in mineral composition. Neither label automatically means coffee-machine safe. Compare the water with the manufacturer’s stated requirements and avoid distilled or demineralised water unless the manual explicitly permits it.
Descale when the exact model calls for it
Descaling too late can allow deposits to accumulate; using the wrong chemical or an unnecessary cycle can create its own risk. Use the named product, dilution and sequence in the manual. If the machine calculates a prompt from a hardness setting, make sure that setting reflects the water actually being used.
A defensible routine is simple
Identify the exact model, test or obtain a credible hardness figure, set the machine correctly, record any filter installation date and respond to its documented prompts. Recheck after moving house, changing water source or adding a treatment system. This creates a useful maintenance record without pretending every UK postcode has the same water.
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