This is an update to an article we posted in 2012, which can be found here!
One of the most important elements of brewing coffee is the water you use to brew with. By using cold, filtered water you'll get better tasting coffee that's better for your machine. The reason filtered water is recommended is because harder water with high mineral content harms machines. This kind of water leads to limescale build up, requiring a "descaling" of your machine. By using filtered water you sidestep this issue and get better tasting coffee too. So why not simply use distilled water and remove minerals from the equation entirely? Well, for a couple of reasons!
Machine Health
The biggest reason you should avoid distilled water is the damage it can cause to equipment. Water naturally bonds to minerals, it's why groundwater is so rich in those minerals in the first place. Distilled water removes the minerals, but not the propensity for water to bond with them. This means that water with a low enough mineral content can sit in a machine and leech minerals from its surroundings. When sitting inside a fancy espresso machine, this means that it'll leach the minerals found in the brass, copper, steel, and nickel that make up the pipes, boiler, and reservoir of most machines. Further, some machines use a very tiny electrical charge to determine whether or not there is water in the reservoir. If the water contained is devoid of minerals, it may not pick up the charge and register, triggering the "reservoir empty" light.
But what about flavor?
Coffee Flavor
As we know, coffee extraction is a chemical process. Water that is too hard doesn't have enough "room" for the coffee to bond with the water molecules. Think of a sponge, one saturated with clear water, and the other dry. If you were to submerge the sponge in a bowl of food-colored water, what would happen? While the already soaked sponge would pick up some color, the dry sponge would pick up more. This is similar to what is happening to coffee as it extracts. On the flip-side, too much empty space (too dry of a sponge) will
over-extract the coffee, resulting in a bitter flavor.
The Specialty Coffee Association has determined that a 150 parts per million degree of minerals is the best balance. This provides enough minerals to keep the coffee from over-saturating, but not a hardness that impedes the process. Given all this, your best route to the best coffee is still good ol' fashioned filtered water!
