Tricky one. I don't fully trust it since there's no DI stage, however, I have tested the vending machine water, Kirkland bottled water, and my LFS's RODI water. The LFS RODI and vending machine both had a TDS of 13, Kirkland close at 19. Who knows what the actual difference of what the TDS is between my LFS and vending machine. I often use distilled for top off, but I would use the Glasier if I couldn't make my own, or LFS was too far to make sense.