You might be thinking that the real secret to a great cup of coffee is having access to the best arabica and robusta beans (the two most common types of coffee beans). And, sure, you’re not wrong — good coffee beans are vital to the coffee-making process. But as Wired previously noted, a good cup of coffee is made up of “1.25 percent soluble matter,” meaning the other 98.75 percent is pure H20. Which is a nice way of saying that Kopi luwak — one of the most expensive coffees in the world, selling for between $100 and $500 per pound — is going to taste like dirt unless you’re brewing it with the right type of water.
But figuring out the right type of water requires the basic understanding that there are, in fact, different types of water. Mainly, the types can be broken down into two broad categories: Hard water and soft water. As per Healthline.com, “the hardness of water is determined primarily by the amount of calcium and magnesium it contains.”
To be more precise, Christopher Hendon, a chemistry professor at the University of Oregon, tells me a common measure is that soft water has less than 60 milligrams per liter of total dissolved minerals. “The general rule of thumb is, if you’re coastal, your [tap] water is soft, since the rain water doesn’t sit on/in land for very long,” says Hendon. “But it also depends on the municipal water treatment philosophy in your region. Here in Oregon, pretty much all water west of the Cascade Mountain Range is soft.”
There’s good news, though, for you coastal elite coffee snobs: Hendon says, generally speaking, most tap water — which is typically soft water — should render a perfectly good cup of coffee. “It’s not always true, because you need some minerals, but soft water tends to be good for coffee,” he says. But Hendon does warn that the language of “hard water” versus “soft water” is “too low fidelity” when it comes to brewing. “Controlling for bicarbonate levels is more important than controlling for minerals in ‘hard water,’” he says. “If you reduce the level of bicarbonate in water, which is typical of soft water, then you taste the acids and sweetness of the coffee beans.”
More to his point, according to CoffeeScience.org, “magnesium ions in water aid the extraction of sharp, fruitier flavors, calcium emphasizes heavier, creamy notes. … Magnesium will have the greatest effect on extraction, calcium slightly less and sodium still less again.” Not to mention that said water temperature should be “between 195 to 205 degrees Fahrenheit for optimal extraction,” also per CoffeesScience.org.
In order to lower levels of bicarbonate — the one mineral in water that will ruin a good cup of coffee — Hendon suggests that people use ion-exchange resins (commonly used in purification processes) to target bicarbonate. “This isn’t a terrible way to do it, and this is what’s done in the Brita jugs (along with carbon filtration),” he says. “We also have a product coming to market this month called Peak Water, which is kind of a Brita jug, but for making coffee-brewing water from any starting water.”
Hendon isn’t alone in his water-for-coffee business idea: There’s an entire market dedicated to helping you achieve the ideal type of water for brewing coffee. One such company is called Third Wave Water, which sells powdered capsules that you can add to your jug of water to “dehydrate” your water for brewing coffee.
With regard to Starbucks, or even the fancy coffee shops that have become increasingly popular, Hendon says that most of them try to use soft water even if it’s not ideal for brewing the best cup. “That’s partly because of the machines they’re using — if you have hard water and heated it up, you’ll create limescale in the machines as a result of all the minerals. This can lead to a lot of bad things like, for example, the temperature probe in the machine may stop working, or the limescale will cause the pipes to clog up after extended use.”
If you really want to taste the hard-and-soft-water difference for yourself, Hendon recommends that you try brewing one cup of coffee using Evian and another using Dasani. “Evian is really hard water, which means it’s got a lot of bicarbonate,” he says. “If you brew a cup of coffee with it, you’ll get a heavy duty sort of sludgy-tasting coffee.” Alternatively, he says that if you use the same beans using Dasani — a softer water — the difference will be night and day. “The cup of coffee brewed with Dasani is going to be a light-bodied, more acidic cup of coffee,” he explains. “That’s when you’ll taste the fruitiness in the beans.”