The morning cup of coffee is often the first thing you put in your body after you wake up and it can make or break the rest of your day. For that reason, you want it to have the best possible flavour. Because coffee is 99% water, the most important choice in how you’ll make your morning cup—besides what kind of bean to use—is the water you use. Given that distilled water is often described as the “purest” form of water, you might be wondering: First, and perhaps most importantly, is distilled water safe to drink? And, if so, will using distilled water make a better cup of coffee?
This of course assumes you have a good coffee maker at home already.
What is distilled water?
Distilled water is produced by boiling water into vapour and then condensing the vapour back into liquid in a separate container. Most minerals or other impurities that were in the water will be removed. Thus, the water that is reconstituted from the vapor is purified. The result is water that is substantively free from many pollutants, but also many important minerals. Distilled water has fewer contaminants (though, importantly, it will not necessarily make non-potable water safe to drink), but it also can lack essential vitamins and minerals, meaning that drinking only distilled water over time can actually mean your body is not getting all of the nutrients it needs when you hydrate. Also—and this is the key to answering our second question—removing minerals from the water can also flatten or undermine its taste.
How does distilled water affect the taste of coffee?
Minerals in water are the primary means of retaining flavour, and of preventing water from leeching flavours from the container in which it is stored. For example, if water that lacks minerals is stored in a plastic container, it will take on a plastic taste and may also absorb some of the plastic’s chemicals. Distilled water will also assimilate other compounds, including drawing carbon dioxide from the air and over-extracting caffeine from the ground beans, both of which will increase the coffee’s acidity. These two factors—the undermining of flavour and the increasing of acidity—can ultimately lead to a cup of coffee that is bland or even overly bitter.
In fact, drawing on data from extensive industry studies, the Specialty Coffee Association of America has determined that water containing around 150 parts per million of naturally occurring minerals will produce the most balanced, flavorful, and smooth cup of coffee. Lower mineral content (sometimes referred to as “softer” water), results in bitterness and flat flavor. If the mineral content is too high, though, (that is, “harder” water), the coffee will under extract and produce a cup that is sour and weak. Distilled water has approximately 9 parts per million of mineral content or only about 6% of the recommended mineral content.
What effect does distilled water have on coffee-making equipment?
The only benefit to running distilled water through coffee-making machines is that it can reduce the need for cleaning. (Some websites claim that distilled water causes physical damage, such as pitting, to copper or brass elements, but this is not true.) Because distilled water is stripped of magnesium and calcium—the primary minerals, unfortunately, that allow water to retain flavor—using it in your coffee maker will result in less build-up of minerals in the internal mechanisms and reservoir. This is why distilled water is recommended for use in other appliances, such as steam irons and hot water urns. In coffee makers, though, the trade-off is probably not worth it; after all, regularly decalcifying scale from inside the coffee maker is a fairly simple and straightforward process .
In some coffee makers, distilled water is actually harmful to the machine. This is particularly true in espresso makers or other coffee makers that have autofill boilers. These boilers rely on a probe that, when in contact with the mineral content in the water, senses the water (because the content conducts electricity) and automatically stops filling. Because distilled water is stripped of minerals, it is non-conductive, which means that the probe will not activate, and the boiler’s autofill function will not turn off. Always consult the manufacturer’s instructions to determine whether distilled water is safe for your coffee maker.
So, to return to the two initial questions, is distilled water safe to drink? It can be, though not in too great a quantity. And will it make coffee taste better? Probably not.
