Deionized and steam distilled are not the same thing. For critical use, I'd only opt for the latter. And since they cost exactly the same in the
supermarkets around here, there's no sense getting anything but the real deal. Our tap water here happens to be quite good, so works perfectly well for ordinary developers, fixers, etc. I always use true distilled for the final film rinse, or during heavy storms when they might
add some excess chlorine to the tap water, or for anything potentially fussy like stock dev or dye concentrates sensitive to either pH or
organics. Ironically, the "drinking water" from the same bottling companies is basically tap water which has first been deonized and had the chlorine taste removed, then has certain minerals selectively added. Seem that pure water tastes odd to most people.