is not Aquarius?
In terms of Elements, Pisces and Aquarius would both fit water extremely well, but Aquarius is actually an air sign (with Gemini and Libra) in standard astrology while Pisces is a water sign (with Cancer and Scorpio). Aquarius might be the weakest connection of the 12 on a surface level (lol) but it does still make sense
EDIT: Did some research, out of curiosity - in mythology, Aquarius was placed in the sky by Zeus after life as the hero Ganymede. In some versions, Aquarius was at one point kidnapped by Zeus in the form of an eagle - as such, Aquarius is associated with the non-zodiac constellation Aquila, the Eagle. So if you want a stronger Aquarius-Air bond, that's probably it.