Makes me want to go to the ocean and start filtering out water somehow.

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