Tool
Water suitability helper
Enter what your test kit or water supplier says and get an interpretation: scale risk, likely effect on taste, and which kind of treatment is worth investigating.
Moderate scale risk
Moderately hard, Moderate alkalinity
Scale will form gradually. Descaling on a normal interval should keep ahead of it.
Alkalinity is in a range that usually leaves coffee tasting balanced rather than either flat or sharp.
Worth investigating
- Nothing, on these numbers. Water in these bands is a reasonable starting point and other variables will matter more
This interprets numbers; it does not tell you what to add to your water. CoffeeHQ publishes no mineral recipes — water intended for drinking must stay safe to drink, and anything mixed for consumption should follow food-grade product instructions and local drinking-water guidance rather than an internet recipe.
Ranked guidance, not a diagnosis
How it works
Hardness and alkalinity are placed into bands, and the bands are interpreted separately because they do different things. Hardness mostly governs scale; alkalinity mostly governs how much of the coffee's acidity is neutralised, which is why high-alkalinity water makes coffee taste flat. The combination then points at a treatment category, never at a formula.
What the inputs mean
- General hardness
- Calcium and magnesium, usually reported in ppm as calcium carbonate or in degrees. Your water supplier publishes this for your area.
- Alkalinity
- Also called carbonate hardness or KH. It measures the water's capacity to neutralise acid, which is a different property from hardness and often the more important one for taste.
- TDS
- Total dissolved solids, from a conductivity meter. Useful for spotting change and comparing waters; it does not tell you what the dissolved material is.
Worked examples
A hard-water area in the south-east of England
- Hardness 280 ppm
- Alkalinity 220 ppm
Result: High scale risk and a strong flattening effect on acidity. Worth investigating filtration or a softening cartridge, and descaling on a short interval.
Common mistakes
Treating TDS as hardness
Two waters reading the same TDS can have completely different hardness and alkalinity, and will behave differently in both the machine and the cup.
Softening water as far as possible
Water stripped of nearly all minerals extracts poorly and can be aggressive to some machine components. The aim is treatment, not purity.
Assuming a filter jug removes the need to descale
It slows scale formation. Descaling still belongs on the schedule.
What the result does not mean
- This interprets numbers. It does not tell you what to add to your water, and CoffeeHQ publishes no mineral recipes — home-formulated drinking water has real safety boundaries.
- A water in a comfortable band does not guarantee good coffee, and a water outside one does not prevent it.
What this does not account for
- Bands are broad and interpretive. Two waters in the same band can behave differently depending on what the minerals actually are.
- Scale risk is about heated equipment, not about whether the water is pleasant to drink.
- Your supplier's published figure is for the supply area and may not match what comes out of your tap after the building's own plumbing.