Is the Etruscan word for lake, "tisś", derived from the word for water, "thi"? The Etruscan word "tina" (a type of a vessel) is, as far as I know, thought to derive from "thi", even though there is an apparently unexplained change from 'th' to 't'.
EDIT: I don't think @Draconis answer to my previous question answers this question. Draconis wrote that "tusna" (swan) is probably related to the Proto-Italic word for "white", and is therefore unrelated to "tisś" (lake). That tells us nothing about whether "thi" (water) and "tisś" (lake) are related.