Is Reverse Osmosis (RO) water the best water for brewing coffee?
Some people say so. As a matter of fact, they RAVE about their coffee since they had an RO system installed. Of course, it all depends on what their water tasted like before they got their system.
Other people say that spring water is the best water for brewing coffee. The problem is, some coffees, such as espresso, taste best with less minerals in the water; while other blends, such as lighter roasts, need oxygen and metallic ions to extract flavor from the coffee grounds. Still other, darker brews can actually mask the attributes of water, so that it doesn’t really matter.
It really depends on the type of coffee you like and what kinds of minerals are in your water. RO water is probably best for espresso and darker roasts. To be safe, if you like your coffee on the light side, brew it with spring water. Otherwise, Reverse Osmosis water is fine, and possibly best.
What about water filters or filtration systems that are built into some coffee makers?
As with any filtration system other than RO, the filtering out of chlorine and other harmless chemicals may affect the taste of the water. But they will not significantly change the mineral and oxygen content, which affects the taste of coffee the most. Combined with an RO filtration system, you should be able to achieve the flavor you desire.
There’s an interesting side story to this: most bottled water companies use Reverse Osmosis to manufacture what they call “spring water.” However, bottled water companies add oxygen and metallic ions to the water just before they bottle it. There are commercial RO units that add oxygen and metallic ions to coffee shop water after the RO process, but they are expensive and not intended for home use.