Looking at the etymology of "equanimous":
1600–10; < L aequanimitās, equiv. to aequ(us) even, plain, equal + anim(us) mind, spirit, feelings + -itās -ity
"aequus" sounds a lot like "aqua"... and I can see how calm water is even and plain. is there any relation between the two? if not, where does each come from, if they can be traced further back?