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Coffee has only two ingredients: coffee beans and water. The type of coffee beans you’re buying, their quality, and provenance certainly figure into the equation, but isn’t it time we pay a little attention to the other ingredient too? That’s right—the quality of water you use to brew your morning cup is just as important as the beans themselves, and it can make the difference between a good and a great start to your day.
Despite its strong flavor, brewed coffee is still about 98% water: It takes only a small percentage of flavor compounds extracted from the beans to make our favorite beverage as strong as we like it. But one of the keys to making sure you’re extracting the right amount of those compounds is to use the best possible water. Let’s take a look at what that means.
Water might be clear, but that doesn’t mean there isn’t stuff in it: Potable tap water in the United States generally contains trace amounts of dissolved substances, both those that are introduced naturally during the water’s journey from its source, and those that are added to make it safe to drink. What these substances are—such as minerals like fluoride and calcium, and sometimes purifying chemicals such as chlorine—and how much of them are in the water system will vary from place to place. (Have you ever traveled somewhere else in the United States and marveled at how different the tap water tasted? These substances are why.) This variation can affect both the water itself and its relationship to the process of brewing coffee.
The specific cocktail of compounds that are already present in your water before you add it to the grounds in your brewer will make a difference in how the coffee flavor transmits, as well as its texture and complexity. Calcium and magnesium, which naturally occur in most drinking water, can aid in extraction because they bond with some of the organic acids in coffee that create a more complex-tasting cup: While calcium is thought to highlight brighter fruity flavors, magnesium draws out sweetness and floral notes. But water that’s too hard—meaning it has a significantly higher calcium and magnesium content—can react with coffee’s acids and leave you with a cup that tastes flat or chalky. Meanwhile, water that is too soft, or lower in those minerals, can produce sour flavors, since the water lacks minerals that bond easily with certain flavor compounds. It may also yield a cup that has a slightly slimy or watery texture.
Water quality also affects the longevity of your equipment and may affect how much effort you need to put into cleaning and maintaining your coffee-brewing gear. Harder water can result in a residue deposit of limescale inside your kettles, brewers, and the internal parts of your countertop espresso machine. Limescale is especially dangerous to electronic brewing equipment because it can interfere with the temperature probes and gauges that allow them to function accurately and safely. It also looks a little gross, not unlike the white buildup that forms on showerheads in regions with harder water. The good news: Limescale is relatively easy to remove with a citric acid solution. Just mix two tablespoons citric acid into each liter of water needed to fill. For a kettle, soak for 10 minutes and then scrub clean as usual. For a coffee brewer, run the solution through a brewing cycle (without any coffee, of course), then flush through with a plain water cycle.
Soft water will have less negative impact on brewers and kettles over time, though the slight sliminess it can leave behind may make it difficult to tell when your coffee equipment is fully clean.
According to the Specialty Coffee Association’s standards for coffee brewing water, the ideal coffee-brewing water should fall within a range of 50 to 175 parts per million of calcium, with a pH of 7 and zero chlorine present. This range is not only a sweet spot for flavor, but also for the care and cleanliness of your brewers and kettles.
How can you find out about your water quality, and what can you do with it? First things first: Don’t sweat it too much. If you’re already drinking and brewing coffee with your tap water and it tastes great to you, that’s fantastic! There’s no urgent need to fix what’s not broken, and if something was really off, you’d probably be able to tell. That said, if you do want to get water nerdy, you’ve got options.
Testing your water for hardness and chemical composition can be as simple as reaching out to your local water agency: The EPA provides a full list of contact information for state-certified laboratories, many of which will provide home water test kits for free or at low cost. In addition to testing your water for mineral content, an official report can also determine whether there are any contaminants present, such as lead.
You can also test your tap water for hardness and pH at home simply by using the appropriate test strips, which are easily ordered online. I like these simple and inexpensive water hardness and pH strips, but you can also pick up a kit that tests for a combination of these factors and more. If nothing else, the results of these tests might help you design a maintenance schedule to make sure your equipment is clean and operating well without caked-on limescale. While a descaling every six months is reasonable for moderate buildup, harder-water areas may call for a quarterly deep clean instead.
You may not want to go the route of hooking up in-line filters or water hardeners if it turns out that your tap water is less than ideal for coffee-brewing standards—again, if it tastes good to you it’s probably just fine for your coffee—but you can investigate some less-disruptive options if you’re curious about the impact on your morning routine.
A tabletop water filtering jug with an activated charcoal filter can help reduce flavors and odors contributed by additives like chlorine without affecting the water’s mineral content, for example. (True demineralizing requires an external filtration system that is more effective than activated carbon.) Bottled spring water is an option, too, though it’s not especially environmentally friendly: Some brands publish their mineral composition on their packaging or websites so you can experiment with the best fit. Many grocery stores also offer refillable gallon jugs of spring water, which vastly reduces waste.
The super coffee-obsessed approach would be to buy gallons of distilled water from your grocery store and customize them for coffee brewing using a specialized product like Third Wave Water, which contains a precise recipe of dissolvable solids that can create the perfect brewing water from ground zero. (Brewing with straight distilled water is not recommended.)
If nothing else, I hope that learning more about your water can offer a new perspective and appreciation for coffee’s unsung but significant ingredient. It’s one more thing to dial in—and one more way to get closer to the best cup of coffee you’ve ever made.
