I think mine would have to be Water, or if you broaden the definition a bit, liquids in general.
I'm a water sign in both the Western and Eastern Zodiac (Pisces and Water Pig), and on the rare occasions people have tried to guess my sign, they always guess a different water sign (I've been mistaken for a Scorpio twice).
I live in a region famous for rain, the ocean, coffee, beer, and wine. In fact, I work in the wine industry. In art, I work almost exclusively with ink. I drink a lot of tea. My life is dominated by Liquids.