Do Aquarians have a special relationship with water?

no... doesn't everyone? it's called shower thoughts..... has nothing to do with your astrological sign. 

Although they're an air sign, they have the water-bearer symbol.

Aquarius is an Air Sign, not a Water Sign.  I think that when you sit in a bath, you relax and this is what allows ideas and inspirations to enter your mind.  And not because you happen to like baths .. it is all about how much we relax in a situation and are able to clear our mind.

Maybe. While Aquarius is an air sign, it is the "water bearer". (The symbol of Aquarius is literally a lady carrying water from a river to her village.)

One of the key things to understand about astrology is that it is based almost entirely on symbolism. So there may be a relationship with water.

Water typically symbolizes emotion, and Air typically symbolizes the mind. (I like to think of astrology as an art.) The symbolism can be interpreted in a million ways, and they can all be right. It's all up to the person interpreting/experiencing the symbolism.

Probably because you're at your most relaxed in your bath. (Aquarius is an air sign btw).

Astrology is great for making excuses and avoiding personal responsibility. It’s made up.

I think so! :D