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.

There are a variety of ways to do it, but you'd want to be careful that you don't attract attention from your local nuclear regulatory agency.

https://en.wikipedia.org/wiki/Heavy_water#Production_methods