My understanding is that the radioactive water contains primarily tritium, as the heavy stuff is easy to filter, while water molecules that incorporate the radioactive hydrogen molecules cannot be distinguished from regular water.
And the amount of tritium involved is a small fraction of the kg per year that naturally fall into the oceans from the sky, where it's generated by cosmic rays. Also, tritium emits low-level beta radiation that cannot even penetrate the outer layer of dead skin cells. And it has a biological half-life of 7-14 days if ingested.
So, not really dangerous. Releasing it into the ocean would be the logical choice.
