While we realize she does not understand the water Jesus is referring to, there is a strong reflection for me to find myself in reading this story.
She does not know the power and ability Jesus has. She does not look at the circumstance at hand and think anyone could even possibly make this request happen. Jesus makes a request of her, and she is simply showing him the request is literally impossible. She does not yet understand or trust that what Jesus asks of her is actually possible or He would not have asked her to do it. She does not trust that what Jesus asks of her is possible, because of Jesus, to actually be done.
I sit here looking over my life at this time and of the things Jesus has called me to do and pursue in life. I look at my circumstances in life and will almost always wonder how in the world he could expect me to draw from such a deep well without a pail. Life is not exactly conducive to what you are saying, Jesus. Those things are literally impossible.
It is easy enough to think, "I only doubt myself, but not Jesus." But if I am honest, I do not doubt myself. I know what I am capable and incapable of. Suddenly I am stricken with the reality that I do not trust Jesus.