Oh yes please coffee with legionaires disease.. lovely!
The Legionaires implications come from the storage of tepid water. So maybe an immersion set up ? And on demand hot water system couldn't possibly be an incubator for Legionaires, in this country at least !!!
But what about the heated water that might then be left to sit about in the hose?
I could be wrong.. but drinking deionized water is just as stupid.
I think the issue with dionised water is if you have polished it off with resin before you drink it. Resin is a chemical wash.
At one time we bought resin from a supplier who assured us that it was FDA approved so suitable for human consumption. I only ever drank the water from the tank once and it tasted terrible. After we finished the first bag of FDA approved resin we bought the ordinary stuff.