Most people don't know what that but you are 100% correct.
I do 2 things to earn a living. I'm an IT Consultant and I operate a maple farm. We use Reverse Osmosis to separate most of the water from the maple sugar crystals. For me, pure water is the waste and the rest is my base product that I boil later.
My small RO machine can produce around 800 gallons of pure water in an hour depending on the pressure I apply on the membrane. With a properly maintained membrane, only H2O is produced, no viruses, no bacteria and no antibiotics can get beyond the membrane.. So yes, it is purer than well or tap water even the natural minerals are removed (they need to be re-added later). The pure water then created will often get polluted by the distribution pipes themselves however.
I would have no problem at all drinking waste water from Reverse Osmosis Filtrate.