Tritium is an isotope of Hydrogen. I believe it has two neutrons in the nucleus as opposed to Deuterium which only has one. Heavy water has an isotope of hydrogen instead of Hydrogen in its atomic structure. So tritium could be a componet of heavy water, but I think Deuterium is more common.

Speak softly and carry a big lightsaber.
Old Jedi never die; they just fade away.