What Water to Use in an Espresso Machine

It helps to separate the two problems, because the ideal water for each pulls in opposite directions.

• Taste.Dissolved minerals — principally magnesium and calcium — are what allow water to extract flavour compounds from coffee. Water with almost no minerals in it extracts poorly and tastes flat and hollow, which is the single most surprising thing about this topic to most people. Alkalinity separately acts as a buffer, damping the acidity in the cup.
• Scale. Those same calcium and magnesium compounds precipitate out when water is heated and deposit inside the boiler, the thermoblock and the plumbing. Scale insulates the heating element (so the machine runs cooler than it thinks), narrows the water path, and eventually seizes valves. Our descaling guide covers what that failure looks like.

So you are looking for a middle band: enough mineral content to extract properly, not so much that the machine furs up. That band has been written down.

The Specialty Coffee Association's published standard Water for Brewing Specialty Coffee(Statistics & Standards Committee, revised 21 November 2009) sets out target values and acceptable ranges. These are the numbers everyone else is paraphrasing, so here they are as printed:

The standard notes that the target is the most desirable point in the acceptable range, while anything falling inside the range is considered to meet the standard — the variances exist to accommodate real-world circumstances.

This is the advice that sounds clever and is not. If minerals cause scale, remove the minerals — no scale, ever. The problem is that machine manufacturers specifically tell you not to.

Breville states it plainly in the instruction book for the Barista Express (BES870XL): "We recommend using cold, filtered water. We do not recommend the use of de-mineralized or distilled water or any other liquid as this may affect the taste of the espresso and how the machine is designed to function."The same wording appears across Breville's espresso range.

Two things are packed into that sentence. The first is taste: water with essentially no dissolved solids sits far below the SCA's 75 mg/L acceptable floor and extracts poorly, giving a hollow, flat shot. The second is the machine itself — that phrase "how the machine is designed to function" is doing real work, because many machines rely on water conducting electricity to sense water level and control heating. Water stripped of its dissolved solids conducts poorly.

Reverse osmosis water has the same problem unless it is remineralised afterwards. RO strips nearly everything out, so straight RO is closer to distilled than to drinking water. If you are on RO at home, the answer is a remineralisation stage or a purpose-made mineral additive, not the RO tap on its own.

Four ways, from most to least precise. Any of them is better than guessing.

1. Your water utility's annual quality report. In the US these are published and free, and they list hardness and TDS for your supply area. It is the most accurate free number you will get.
2. Cheap hardness test strips.A few dollars, results in seconds, accurate enough to tell you which band you are in. Some machines — Breville's Dual Boiler among them — ship with a test strip precisely so you can set the machine's hardness setting correctly.
3. A TDS meter.Reads total dissolved solids directly, which is the number to compare against the SCA's 75-250 mg/L range. It does not separate calcium hardness from everything else, so pair it with a strip.
4. The kettle test. Free, and surprisingly informative: if your kettle furs up quickly, so will your espresso machine. Look inside it now. This is also the best rough guide to how often you will need to descale.

Start with a carbon filter jug. It is cheap, it removes chlorine, and crucially it does notstrip the minerals you want. For most households on soft to moderately hard water, tap water through a filter jug is genuinely the right answer, and it is what Breville's "cold, filtered water" wording points at.

If your machine takes its own cartridge, use it.Breville, Philips (AquaClean) and Jura (CLARIS) all sell filters designed around their own machines — Breville notes that the provided water filter helps prevent scale build-up. This is the least-effort correct answer, because the filter is sized for the machine's flow rate and the machine often tracks it for you.

Bottled water works if you read the label.Look for a bottled spring water quoting a dry residue or TDS figure in the SCA range — roughly 75 to 250 mg/L, ideally near 150. Avoid anything marketed as mineral water with a high mineral content, which will scale a machine fast. It is an expensive and wasteful way to run a machine daily, but it is a reasonable stopgap if you are on very hard water and waiting for a filter to arrive.

The one to skip is at the bottom of the table, and the reason is in the section above.

If your house has a water softener, do not assume that solves it. Conventional ion-exchange softeners work by swapping calcium and magnesium for sodium. That does reduce the hardness that causes classic limescale — but it does not reduce the total dissolved solids, and it raises the sodium content of the water.

Look back at the SCA table: the sodium target is 10 mg/L, "at or near". Softened water routinely sits well above that, which is why softened water often tastes slightly flat or faintly salty in coffee even though the kettle stopped furring up.

The practical answer in a softened house is to take water from an unsoftened tap if you have one — many installations leave the kitchen cold tap unsoftened for drinking — and run it through a carbon filter. Failing that, bottled water in the right range for the machine is a defensible compromise.

A water filter cartridge that has not been changed is not a filter; it is a piece of saturated carbon sitting in your water tank. Breville's own procedure for the Barista Express is explicit about the interval: rinse the filter and mesh, soak the filter for five minutes, place it in the holder, install it in the tank, and set the date dial two months ahead.

Two months is the manufacturer's figure, and on hard water Breville advises changing the filter more frequently than that. Put it in your calendar, because the machine will not always remind you and the cartridge gives no visible sign of being spent.

One more line from the same manual, which almost nobody follows and which costs nothing: "Always check the water level before use and replace water daily." Water left standing in a tank for a week is not what you want in a shot.

We do not currently have a water filter pick in our own product picks, so we are not going to point you at one we have not written up — buy the cartridge your machine manufacturer specifies, which is the correct answer anyway.

Good water from today stops scale getting worse. It does not remove what is already in there, and if your machine has been running on hard unfiltered water for a year or two, there will be some. The symptoms are a machine that takes longer to heat, brews cooler than it used to, flows more slowly, or has started making unfamiliar noises.

That is a descaling job, and it needs an acid descaler rather than a general cleaner. Our full descaling guide covers the cycle, the intervals by water hardness, and why vinegar is a false economy. These are the products it uses.

For most machines,a purpose-made descaler with published directions. Urnex Dezcal is the standard choice and comes in a two-pack, which is roughly a year's supply on moderate water.

For Breville owners,a solution formulated for Breville's own descale cycle — the one that runs when the CLEAN/DESCALE light comes on and stays on rather than flashing.

And the other half of the job.Descaling removes mineral deposits from the water path. It does nothing about coffee oils in the group head and shower screen, which is a separate cleaner and a separate cycle — a distinction the flashing-versus-solid light on a Breville is actually telling you about. Our cleaning guide covers backflushing.

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Then fix the water, so you are not doing this again in six months. For a shared or office machine, where descaling reliably never gets scheduled, filtration from day one matters even more — see our office machine guide.