Water affects espresso and filter coffee in different proportions.
The flavour side
Filter is more sensitive. A cup is 98.5% water, brewed slowly, with delicate aromatics that alkalinity flattens easily.
Espresso is less sensitive. It is 88 to 92% water, far more concentrated, and the coffee dominates more. The differences are real and smaller.
If you are going to invest in recipe water for one method, invest for filter.
The machine side
Espresso is far more sensitive. An espresso machine has a heated boiler under pressure, and scale accumulates on the element and in narrow passages.
Filter brewers are cheaper, simpler, and easier to descale.
Hard water will destroy an espresso machine in a few years. It will inconvenience a pour-over setup not at all.
The practical consequence
For an espresso machine, filtration is not optional. It is the difference between a machine lasting five years and twenty.
Never use very soft or RO water in a machine either — several problems follow. Water-level probes on many machines work by conductivity and fail with near-pure water, and low-alkalinity water can be corrosive to copper and brass.
The target for espresso
Moderate hardness — 50 to 100 ppm — for extraction, and low alkalinity for taste.
Not zero. Machines want minerals present, just not many.
The simple rule
Filter for the machine. Refine for the filter brews.
Last reviewed 8 August 2026