The handwriting on the list of water sources changes between shots.
The studio lighting rig is reflected in the Doctor's glasses when he examines a pair of test tubes.
As Ian, Susan and the First Elder wait for the antidote, a boom microphone drops into shot and casts a shadow across the First Elder's head.
When The Doctor and Carol are with John, after the antidote has been sent off to Ian, the camera pans up slightly and we get a brief glimpse of a boom mic before it zooms in again.
First Elder: "Give my Doctor the congratulations." Presumably, the "my" and the "the" should be switched.
At 22:58 the Second Elder says "viaduct" when he means "aqueduct".