Water for coffee
Water can be a confusing topic. For example, as I've mentioned in "The Professional Barista Handbook" and "Everything but Espresso," "alkalinity" and "alkaline" mean different things. Machine manufacturers focus on preventing limescale buildup and scaling, but they are generally unaware of optimal water chemistry for flavor, or how to balance limescale prevention concerns versus optimizing flavor. Furthermore, the industry's historical emphasis on Total Dissolved Solids (TDS) has led to the misconception that a reasonable TDS level means this water is ideal for making coffee.
I'll try to simplify the discussion to help coffee shops, baristas, and roasters make decisions about water quality. The key points to cover are:
- Alkalinity is the most important factor in how water affects the flavor of coffee.
- It's essential to perform a water analysis in a laboratory to determine which water treatment system is best suited for a coffee shop or roastery. Test, don't guess.
- In addition to flavor, it's important to ensure that the water won't cause limescale and scale buildup in your coffee machines. This is especially important in high-volume environments, such as coffee shops. Sometimes, compromises are necessary, allowing for a little limescale and scale buildup or sacrificing a little flavor quality to balance these two concerns.
Some definitions
TDS: Total Dissolved Solids. This means exactly what it sounds like: the amount of dissolved substances in the water. Historically, industry recommendations have been to use water with a TDS between 100 and 150, but TDS alone is a relatively unimportant number.
Hardness / General Hardness / Temporary Hardness / GH: This refers to the hardness caused by the dissolution of calcium, magnesium, and iron ions. GH can affect flavor and the risk of limescale formation, but there is little consensus on optimal levels or the ideal balance between Ca+ and Mg+.
pH / Potential of Hydrogen: A measure of acidity on a scale of 1 to 14. 7 is considered neutral. The pH scale is famously confusing since it's logarithmic. In other words, a pH of 2 is ten times more acidic than a pH of 3. Coffee, with a pH of around 5, isn't that acidic, despite its reputation. For reference, lemon juice (pH 2) is a thousand times more acidic, and stomach acid can be even more acidic than lemon juice. The pH of water isn't a particularly important factor when considering water for making coffee, as alkalinity levels have a much bigger impact on the final acidity in the cup.
Alkaline: This simply means that the pH is above 7, indicating that the water is "basic" and not acidic.
Alkalinity / Bicarbonate / Buffer / Carbonate Hardness / KH: As you can see from these terms, whoever created the nomenclature for water chemistry must have been a misanthrope. Alkalinity is a solution's resistance to becoming more acidic when an acid is added. Alkalinity is by far the most important factor in how water chemistry will affect the flavor of coffee. In simple terms, higher alkalinity makes coffee less acidic, and lower alkalinity makes it more acidic. These statements are true regardless of the water's pH.
My personal preference for a well-developed, light-roasted coffee is an alkalinity level of 30 to 40 ppm. Your preferences may differ, and you may intentionally choose unusual alkalinity levels at times to enhance or reduce acidity, depending on the type of coffee and the degree and quality of the roast. For example, you may choose water with a low alkalinity to enhance the acidity of a flat-flavored coffee, etc.
Keep in mind that water can have high alkalinity, but not be alkaline. As I mention in "The Professional Barista Handbook" (2008):
"A solution can be very alkaline but have low alkalinity, and vice versa. As an analogy, think of alkaline as the solution's location on a political spectrum. Let's say alkaline refers to being on the right and acidic to the left; alkaline denotes being conservative, acidic denotes being liberal. (This is not a political comment!). Alkalinity, on the other hand, is analogous to stubbornness, or resistance, to becoming more liberal. Of course, one can be at either end of the spectrum (acidic or alkaline) and still be resistant (having high alkalinity) or prone (low alkalinity) to becoming more liberal."
Water for making coffee at home
If you make coffee at home, there are some convenient options:
1. Look online for your city's municipal water quality report. It can help you determine if your tap water's alkalinity level is high or low, or if the water contains contaminants you want to avoid that can only be removed through reverse osmosis. Knowing your tap water's chemistry will help you make an informed decision about how to optimize it for making coffee. 2. Bottled Water: I've never been anywhere in the world that doesn't offer at least one bottled water option that's good enough for making coffee. It's worth reading labels and searching online to learn more about bottled water options in your area. If you can't find bottled water with your preferred alkalinity level, consider blending distilled water with other bottled waters to achieve your alkalinity goal. 3. Buy demineralized or distilled water and add dry salts or a product like Lotus Water Drops. This can be a good way to learn about the effects of water chemistry on coffee flavor and help you fine-tune your preferences. Many grocery stores sell inexpensive reverse osmosis water that you can purchase and pour into reusable pitchers. 4. If your tap water is naturally good for making coffee, you may be able to use a simple carbon filter, such as a Brita pitcher or similar. If your water is hard and/or has very high alkalinity, you can try the Peak Water pitcher or another similar product.
Water for coffee in a commercial setting
If you consult machine manufacturers, they will correctly advise you on the water treatment that will protect your machines from limescale (CaCO3) buildup. However, most manufacturers or service centers are unaware of the water chemistry that makes coffee taste better.
A simple way to estimate the limescale buildup potential of water at various temperatures is to use an online Langelier Saturation Index (LSI) calculator. I've mentioned the LSI in several of my books.
For many years, I fought with my espresso machine supplier because they insisted I use a water softener to protect the machine. I argued that I didn't need a softener since my water didn't cause limescale buildup in the machine, and softening very hard water would damage the flavor of the coffee, so a softener is never the best solution. They finally relented when I showed them the LSI.
In more recent years, the industry has eschewed the risks of water softeners and favored reverse osmosis systems with mixing valves. These systems remove approximately 90% of dissolved solids from water through reverse osmosis and offer the option of mixing reverse osmosis water with activated carbon-filtered tap water.
Let me show you an example of how to use a reverse osmosis system with a mixing valve. Let's assume your tap water has:
80 TDS
60 GH
60 KH
but you prefer an alkalinity (KH) of 30.
Reverse osmosis water will have a KH of 6 (we'll assume it removes 90% of the dissolved solids in the water). "Mixing water," which has only passed through a carbon filter, will have a KH of 60.
If you use 55% reverse osmosis water and 45% blend water, the result will be:
.55*6 + .45*60 = 3.3 + 27 = 30.3 KH
Keep in mind that while reverse osmosis systems are common in coffee shops, they are not appropriate in places with soft tap water. For example, a coffee shop in Manhattan may have water with 25 TDS and 15 KH. Removing any minerals from this water would be a mistake, and the coffee shop should only use a sediment filter + carbon filter to remove unwanted flavors and odors.
Test, not guess
I always ask my clients to have their water tested at a lab before choosing a water treatment system. I have labs I trust, and I personally prefer to pay $100-$200 for a test rather than get a free one from a water treatment company, partly so I don't feel beholden to that company and partly to get a complete analysis, which few, if any, water treatment system companies provide for free.
For example, below are the results of the water analysis on the Prodigal roaster. As you can see, the alkalinity is slightly above my preferred range, but close enough to that range that I don't think a reverse osmosis system is worth the effort. We were satisfied with the coffee flavor after simply passing the water through a sediment filter and a carbon filter.
About Scott Rao
Scott Rao is one of the leading figures in the world of specialty coffee. He is the author of several books, including "The Professional Barista's Handbook," "Everything but Espresso," and "The Coffee Roaster's Companion," all written with the aim of helping the industry pivot toward a more educated and scientific understanding of coffee. He devotes much of his time to consulting coffee roasters around the world, teaching master classes on coffee roasting, and designing cutting-edge coffee equipment.
At Ineffable Coffee, we've been working with Scott since 2018. His advice and experience over the years have been invaluable. As a result of this collaboration, we're pleased to offer this content in Spanish with his full consent.
Article written by Scott Rao and originally published on his blog
