What Water Hardness Means for an Espresso Machine

Hardness is a measure of dissolved minerals in water. Mostly it means calcium and magnesium.¹ Hard water has a lot of them, and soft water has few. That's the whole idea.

Where the minerals come from

Rain doesn't start out hard. As water moves through soil and rock, it dissolves small amounts of naturally occurring minerals and carries them along.¹ Limestone and chalk are common sources.²

So hardness depends on where you live. The USGS notes that water hardness varies throughout the United States.¹ Two houses in the same state can get quite different water, and the same goes for other countries.

What the labels mean

Water scientists sort water into bands. The USGS guideline calls water soft when it measures up to 60 mg/L as calcium carbonate, and moderately hard from 61 to 120 mg/L.¹ Above that you get "hard" and "very hard." Those numbers can show up in other units, which is why the units page exists.

You can't judge hardness by looking at a glass of water. It looks clear either way. Usually you find out from a report, a test or a lack of soap foam.²

Why an espresso machine cares

Heat is the issue. Hard water is often noticed by limescale forming in kettles and water heaters.² An espresso machine heats water too, so the same minerals can settle inside it. The scale page shows where.

One maker's support article puts it plainly: hard water can contribute to mineral buildup inside your machine over time.³ The same article says buildup can affect brewing flow, temperature and machine performance.³

Wikipedia adds a general point about equipment. Hard water also forms deposits that clog plumbing.² A small machine has narrow passages, so that's worth keeping in mind.

Softer isn't always the goal

It's tempting to think the purest water is the safest choice. Makers don't always agree. That same Breville article says to avoid water with little or no mineral content, such as distilled or demineralized water.³ Your own manual may say something different, so read it. The manual page shows where to look.

The article also says water recommendations can vary by machine and local water hardness.³ In other words, there's no single answer for every kitchen.

What to do first

Before you spend money on filters, strips or descaler, find out two things.

• How hard your water is. The utility report page and the test strip page cover the two ways to learn that.
• What your maker says about water. That's the rule that counts, because it comes from the people who built the machine.

With those two answers, the rest of the decisions get much simpler. A filter, a different water source or just a regular descaling routine will all make more sense once you know your starting point.