One profile can serve both, with a small compromise at each end.
What filter wants
Lower alkalinity — around 40 ppm or less — to preserve acidity and clarity.
Magnesium-forward hardness for aromatic extraction.
Filter brewing is more sensitive to water, and it benefits most from optimisation.
What espresso wants
Similar hardness, and it is less sensitive to the profile because the drink is concentrated and the coffee dominates.
Some alkalinity matters more here — near-zero alkalinity water is more corrosive to a boiler.
Low enough hardness to prevent scale, which is the real constraint.
The compromise
Hardness 50 to 100 ppm as CaCO₃, magnesium-favoured. Alkalinity around 40 ppm.
That sits comfortably in the SCA range and serves both. It is what most commercial installations run.
When to split
Competition-level filter brewing, where people go lower on alkalinity than a machine would tolerate long-term.
A plumbed espresso machine, where the machine water is fixed by the installation and filter water can be built separately in a jug.
The practical setup
One filtered supply for the machine, and recipe water in a jug for pour-overs if you want to optimise.
That is cheaper than two filtration systems and it puts the effort where it pays.
The thing not to do
RO or distilled water in an espresso machine. Corrosion, and level probes that stop working.
Last reviewed 8 August 2026