Brewing water is just as important to a delicious cup of coffee as the coffee itself. This is why cafes spend $10k or more on a water treatment system. These systems first filter everything out of the water, using a reverse osmosis process, and then add dissolved minerals back to the water at just the right right ratio for optimal taste and brewing. These dissolved minerals not only ensure that the brewing water tastes good, but also impact extraction, flavor and mouthfeel.
Scott Rao’s book “Everything But Espresso” is dedicated to coffee brewing techniques, and includes a chapter on water chemistry. Rao notes that water with too high of a pH will taste dull, whereas water with too low of a pH will be brighter and more acidic. Brewed coffee will taste muddled if TDS values are too high, and it will lack mouthfeel and refined flavors if TDS values are too low.
The Specialty Coffee Association of America (SCAA) has developed a water quality standard, which seeks to define the optimal water chemistry for coffee brewing. The table below details the SCAA’s target values and its acceptable range for brewing water characteristics, as well as the composition of two readily available bottled waters, as reported in the manufacturer’s water quality report, and the composition of our local tap water, as documented by the City of Austin:
While the water chemistry of these bottled waters does not match the SCAA target values, I find coffee brewed with Gerber Pure or Nestlé Pure Life consistently preferable to coffee brewed with our local tap water, even if I filter the chlorine out of the tap water first. The difference is not subtle, either.
You can easily evaluate your brewing water preference at home. Simply purchase something like Gerber Pure—which is available at CVS, Target, Walgreens and Walmart—and brew up identical cups of coffee using bottled water on the one hand and (filtered) tap water on the other. Polished immersion brewing is particularly well suited for this type of evaluation, since it is easy to duplicate brewing parameters. You may also want to try other types of drinking water or spring water. However, some bottled water formulations vary across a year. (Gerber Pure is consistently formulated to published standards, because it is specifically made for mixing with baby formula.)
If you are looking to brew with water that more closely matches the SCAA water quality standard without investing in a home water treatment system, Global Customized Water offers a 2-part brewing water formula designed for traveling baristas. You simply add the two vials to distilled or reverse osmosis water and voila—you have optimal brewing water.