I've never worked with Mili-Q, but the college I went to did it's own that it collected from rain water. What I recall, the TDS
of this was really close to 0 if not 0. But that was for a reason I'm sure, but there wasn't a DI
resin phase like we run to make that final jump from ~10 to 0.
I would use it if it was being offered up to me. If you are concerned about it, I'm sure there is a TDS
meter somewhere in one of the departments that someone will let you use without issue. And if you do so, report the results. Would love to know.