Why water matters for a home espresso machine

Water is the one ingredient in a shot of espresso that you don't buy at a coffee shop, and it travels through every part of the machine's water path. A maker of home machines puts it plainly: the water you use can affect the taste of your espresso, mineral buildup, and how the machine operates¹.

Two things water can do

It can leave deposits inside the machine. Tap water carries dissolved minerals. When the machine heats that water, some of those minerals can stay behind as a crust. The crust has a name, limescale. It's a hard, chalky deposit made mostly of calcium carbonate².

Water that's rich in calcium and magnesium is called hard water. Those two minerals are what cause hardness, along with a variety of other metals³. The page on what water hardness means explains how it's measured.

Breville says hard water can contribute to mineral buildup inside an espresso machine over time. It adds that this buildup can affect brewing flow, temperature, machine performance and the taste of the espresso¹.

It can change the taste. Breville links the water's mineral content to the cup. It says water that lacks minerals can contribute to a sour, acidic taste in the espresso¹. So the answer isn't simply "the purer the better."

Why makers care about scale

For one maker, Decent Espresso, scale is a repair problem. Its water guide says the wrong water can lead to scale buildup and heater failures⁴. The company says it can't cover those failures under warranty⁴.

Small tubes and narrow openings are one reason a design can be sensitive to scale. Decent points to its many small tubes and calibrated pressure-restricting orifices as the reason scale matters so much for its machines⁴.

Makers don't all agree

Here's the catch. Breville tells readers to avoid distilled water and other water with little or no mineral content¹. Decent says its machines are built to use reverse osmosis or distilled water⁴.

Both statements are true for their own machines. The designs differ, and so do the rules. That's why the manual for your own model comes first, and why this site keeps pointing back to it.

Decent also ties descaling to the water itself, and its softest-water threshold is covered on the descaling page. Breville takes a different line. It says to descale according to your machine's maintenance instructions and to set the machine's hardness level if it has that setting¹.

Descaling is a fix, not a plan

Descaling means removing limescale, and descaling agents are commonly used for the job². Makers treat it as part of the routine, and each has its own product and steps. The page on descaling and your manual covers where to look.

What to check first

1. Find your machine's manual and read its water section.
2. Find out how hard your tap water is. See how to find your tap water hardness.
3. Compare the two. If the manual names a hardness limit or a water type, that settles it.

Your doctor or your local health agency is the place for any question about drinking the water yourself. This site only covers the machine.