H2O, Hello There: An Introduction to Water for Coffee Brewing
Have you ever taken a bag of beans home from your favorite shop, brewed them according to the recipe printed on the bag, and found the resulting brew to be lackluster and almost completely different from that cup you enjoyed in the cafe? You might wonder if it was the grinder, or maybe your technique was off -- but what if it’s actually something else, what if a tiny pinch of extra magnesium in your water was to blame? This is not an uncommon problem to have, it turns out, as the water we use to brew with can yield very different results from exactly the same beans and brew method, such that two brews can be rendered unrecognizable if the waters used are different enough.
You may be sitting there, skimming the text below and wondering, “how is there *so* much to write about water? Who could be so picky?!” And I certainly wouldn’t blame you for that, it’s an unassuming topic that actually gets quite complicated very quickly. But the basic information I’ve written here will be plenty enough to help you make better coffee at home, and if you’ve ever found yourself frustrated with trying to get cafe-quality results at home, even the simplified recommendations here might be the key to your coffee nirvana.
The water with which we brew our coffee is fundamentally not just water. Chemically, our brewing water is not pure - it contains dissolved minerals, chemicals, and gases, many of which have a noticeable role to play when brewing coffee. While there is certainly more to be learned about specifically how each component affects coffee brewing, we do have a somewhat substantial base of established knowledge about water and coffee already. Practically speaking, the best water to brew with tends to taste and smell quite neutral, so it contributes little in the way of off-flavors to the coffee itself. Scientifically, things get rather more complicated.
In much of the United States, the water coming out of your tap is likely to meet those practical criteria already. Perhaps at worst you have some strange flavors from old metal pipes, an odor of chlorine, or too much calcium or magnesium from hard water. In many cases in the home, you could simply filter that water and be on the right track for brewing coffee with decent to great flavor. If you’re not all that fussy about your coffee and you’re happy with your brewing results, then the chase might end right there.
There are however many exceptions, as a good deal of you are using somewhat offensive tap water that you would hesitate to drink on its own. Whether you’re on a well with funky groundwater, a private water supply not suitable for drinking, or your municipality is simply an underperformer and does not provide satisfactory water for your tastes or needs, you may find yourself needing to treat your water more heavily or needing to skip the tap entirely and find better water to purchase for coffee brewing.
As we mentioned before: what’s in the water we use for coffee can end up being complicated stuff. Other beverage industries like beer and wine have reams of data and decades of knowledge going into the water they elect to use for their products, and while we can learn a few things from what they already know, coffee is still a different beast and is at a younger stage of its overall evolution as a craft product. We do have some useful general guidelines that we can follow: too much mineral content can cause your coffee to suffer in quality, too much alkalinity can cause a soapy taste or residue, overly hard water can taste bitter or chalky, water with very little mineral content can cause all kinds of strange extractions and off-flavors, and can even cause corrosion of your equipment. Some minerals cause scale buildup that can disable or destroy your coffee brewing gear, while others can erode the internal parts until they spring leaks.
The Specialty Coffee Association of America has a simple list of standard criteria for brewing water: it should be clean and free of odors, colors, and off-flavors. It should have a neutral pH (neither acidic nor basic), it should have around 150 mg/L of dissolved minerals, including 4 grains of hardness, about 10 mg/L of sodium, and 40 mg/L total alkalinity. While most of us do not own the testing kits needed to see if our desired water is within those parameters, some bottled water options do in fact list some or most of these metrics, and test strips are fairly inexpensive if you’d like to test on your own. The Water Standards are time-tested and generally well accepted, but don’t necessarily align with some of the more contemporary suggestions established by newer research.
What should you do if you’d rather not fuss over all these details, and simply want to brew a decent cup of coffee? In most cases, you can probably head to your local grocery store and stock up on their cheapest spring water. If it tastes good enough on its own, it’s very likely good enough to use for coffee and you needn’t worry about the minutiae. If you’re thinking you’d like to get really great water but aren’t sure how to approach all the chemistry involved, you can even buy products tailored specifically for coffee brewing - some coffee shops will sell you some of their pre-balanced brewing water, or you can buy some distilled or reverse osmosis water (both are heavily purified with almost no mineral content) and add a product like Global Customized Water’s AB Formula or Third Wave Water to treat the water with minerals specifically balanced for brewing coffee.
Those bespoke water solutions like the AB Formula are not a perfect solution for every coffee under the sun, however. They’re a great way to create a standardized brewing water formula that remains static whether you’re at home or abroad, but you can bet that almost no coffee roaster will be using the same water as you when they develop their coffees and tweak their roasting for certain flavor profiles. So, even though we think they’re good products and quite helpful to folks who need more predictability in their brewing water, they’re not a guarantee to make every coffee taste its best.
Wondering what we wouldn’t recommend? To start, don’t use pure distilled or reverse osmosis (RO) water for coffee brewing. Sometimes these are recommended as they don’t contribute to limescale buildup in drip machines, but they are simply too pure to brew coffee with and you’ll leave a lot of good flavor behind. Also do not use water that doesn’t taste very good on its own. That means that water with noticeable off-flavors like anything chalky, metallic, soapy, or otherwise funky probably won’t do your coffee any favors. Basically, if your water has some minerals dissolved in it and tastes and smells good and clean, you're off to a pretty good start. We would also caution you to use a softener for any water being used in espresso machines, to prevent damage due to limescale buildup.
If you want to dive deeper down this rabbit hole, that’s a whole ‘nother blog post! (Coming soon)