TDS — total dissolved solids — is a rough measure of everything mineral in the water. For coffee it is a useful shorthand and it hides an important distinction.
The numbers
The Specialty Coffee Association’s target is around 150 ppm total dissolved solids, with a working range of roughly 75 to 250. In practice most brewers aim somewhere in the 75 to 150 band.
Below about 50 ppm, extraction suffers noticeably and the cup tastes thin and hollow. Above about 250, the coffee reads as heavy and dull, and the machine scales quickly.
Why TDS alone is not enough
TDS tells you how much is dissolved, not what. Two waters at 150 ppm can behave completely differently depending on the split between two things:
Hardness (calcium and magnesium) — the useful part. These ions bind flavour compounds and carry them into solution. Magnesium in particular is associated with brighter, more defined extraction.
Alkalinity (bicarbonate) — the part you want low. Bicarbonate buffers acidity, so high-alkalinity water flattens the brightness of a coffee and makes it taste dull. It is also what forms limescale.
The ideal is moderate hardness with low alkalinity. That combination is why some 150 ppm water makes excellent coffee and other 150 ppm water does not.
Measuring it
A cheap TDS meter gives you the total in seconds. Splitting hardness from alkalinity needs a drop test kit, which costs a little more and is what anyone serious about water uses.
Is this worth chasing?
For espresso with milk, no — you will not hear it. For light-roast filter coffee, it is one of the last meaningful variables after grinder and beans, and it is genuinely audible.
Questions people actually ask
Is a TDS meter worth buying?
For under twenty euros it is a fair diagnostic — it will tell you immediately whether your tap water is in the right ballpark. It cannot tell you the hardness-to-alkalinity split, which is what actually matters.
What do mineral recipe sachets contain?
Typically magnesium sulphate and a small amount of bicarbonate, dosed into distilled water to hit a target profile. They exist precisely because tap water rarely lands in the ideal range.
Last reviewed 8 August 2026