probably originally attributive use of aqua, or generalized from words in which it is etymologically the head noun of a phrase, as aquamarine, aquatint
The MTA did try something similar on the west side yard of Penn Station: a giant tube full of water known as an aqua dam.
Hurricane Sandy’s Lesson for Flood-Proofing a Subway|Josh Dzieza|November 4, 2012|DAILY BEAST
From Aqua Buddha to Wikileaks, 2010 gave us a bounty of new words for our political vocabulary.
The 2010 Political Dictionary from A to Z|Samuel P. Jacobs|December 12, 2010|DAILY BEAST
Mrs. Brewton took no notice of him, but bade me admire Aqua Marine as far surpassing any other 6-month child.
The Jimmyjohn Boss and Other Stories|Owen Wister
It was the aqua tofana undiluted by mercy, instantaneous in its effect, and not medicable by any antidote.
The Golden Dog|William Kirby
I noticed a woman hurrying out of the tent, and hoped Aqua was not in further trouble—she was still surrounded, I could see.
The Jimmyjohn Boss and Other Stories|Owen Wister
Together with these appeared Bortolo Cer, whose scenes have been engraved in aqua fortis by Boschini himself.
The History of Painting in Italy, Vol. 3 (of 6)|Luigi Antonio Lanzi
“Aqua tofana was not a Bornean poison, my friend,” said Cleek, with a smile.
Cleek of Scotland Yard|Thomas W. Hanshew
British Dictionary definitions for aqua
aqua
/ (ˈækwə) /
nounpluralaquae (ˈækwiː) oraquas
water: used in compound names of certain liquid substances (as in aqua regia) or solutions of substances in water (as in aqua ammoniae), esp in the names of pharmacological solutions