Water is not blue, blue is a reflection of the sky! If it is a specific water then "the water" should be used instead :)
Su renksizdir. = Water is colorless. :)
What means the "-dir" ?
Su mavi vs Su mavidir ?!
It seems that both are correct.
As a daily(!) sentence, we use "Su mavi"; but as a fact, we use "Su mavidir". Right ?