This is the only episode where LeBeau does not appear. He is replaced by the character 'Scotty'. However, Hogan does refer to him when he tells Klink the story about the water coming from a spa in Norway.
Heavy water is not radioactive. The deuterium in it is stable; it does not decay. You'd be in no danger at all from radiation. Heavy water, being (literally) heavier than plain water, performs a bit differently in chemical reactions, but only a little, so you'd have to drink a lot of heavy water for it to harm you.
This is the first time Klink is smoking a cigarette in a cigarette holder.
A 4-second scene where Carter looks at the water and says "It's odorless and colorless" just before he tastes it does not appear in the syndicated version, but was in the original.
Some of the sub-machine guns that the German guards are carrying are in fact U.S. made Thompson M1A1 .45 caliber sub-machine guns, which were never used by the Germans.