A severed head underwater

I just read in Wendy Berg's Red Tree, White Tree an old Arthurian legend about a man who, having dishonored a woman, is killed and his severed head dropped into a well.

The book I read immediately before this one was entirely different in character: Laeth's Powerless, a realistic novel set in Portugal in 2025. But, though any more detailed explanation would constitute a "spoiler," it contains a scene that parallels the above-mentioned Arthurian story remarkably closely.

Come to think of it, "head underwater" imagery also played a central role in Laeth's first novel, Phantasia.