The idea behind distilled or reverse osmosis water use is it is "too clean" of minerals and can actually cause over time removal of copper from boilers, tubing and other parts. Water being the universal solvent it can actually dissolve components to the degree of damage. That is the theory. How long it takes to do such damage I have no idea.

The other issue is some minerals in the water actually will extract the coffee solids better for better tasting coffee. But that doesn't have anything to do with machine life or performance.

We use RO water and mix about four part RO to one of our tap water. I looked up the hardness and what our rural water district had for water specifications and that appeared to be in range of the right amount of mineral in the mixed water to make good coffee yet not cause erosion or excessive buildup in the boiler and components with calcium and iron. Am I right??? Ask me in ten years and I might have an opinion. Our tap water was way too hard (and will cause calcium and iron deposits on stuff) but mixing a small portion of it with pure water looks to be about right. Seems to work.

I watched a number of videos on Youtube about making water for making coffee. There are a bunch of them. You can also buy the minerals and add them proportionately to RO water. Different water is supposed to make the same coffee brewed identically taste different. At least according to the gurus. Tastes like coffee to me. My wife tastes are more discerning. 

https://www.youtube.com/results?search_query=water+for+coffee+machine   #mce_temp_url#