You can centrifuge it. Heavier molecules move closer to the bottom. Repeat until you reach the desired purity.
You need shitloads of ordinary water to extract a liter of heavy water. And I'd be surprised if there's any superheavy water in that, because tritium radioactively decays.
Fun fact: Heavy water is slightly toxic to humans. If you only drank heavy water, you'd die as it shifts the chemical reactions in your body out of balance. A moderate amount is fine though.
IIR, a number of rich & famous people have developed severe mercury poisoning after extended conspicuous consumption of swordfish and other very expensive/very contaminated seafood.
Obviously the luxury bottled water industry is missing out on the potential of D2O and T2O.
Emphasis on the slightly. I believe it would take weeks of only consuming heavy water. You could certainly drink a single glass of it without ill effects.