I think he talks about looking for life. He ends up looking in the wrong places because he got lost in the derailing thoughts of the mind. He is trying so desperately to supply his own strength but it catches up with him. He needs the all-sufficient "water" or life that Jesus has to offer us. I love this song because we all struggle with this: we get trapped in our swirling minds of tormenting thoughts. We try so desperately to fight through this life alone when God is the one who experienced the truest form of torment - death on a cross. His water is all we need yet we still fall into the trap of neglecting the water in an attempt to figure this life out on our own - only to trip through the sand.
Verse One: He explains that he hasn't talked to God in a while because he got lost in himself. He is thirsty for true life.
Chorus: He talks about trying to run through the sand (trials of life) and is gripping to the little water that he has left. Jesus is the water because that is the only thing that is giving him strength to get through the sand. He then gets caught up in the sand again and loses sight of the water. He talks about doing his best and it is the only thing he can do - and even when he tries his best he still loses it. He needs the water.
Hook: He talks about how he is an addict with a pen, so someone who is addicted to writing to sort out these thoughts that swirl around in his brain, sending him back and forth with himself and God. He wants the tormenting thoughts in his brain to end and screams out to God that he wants to be washed with the water.
Outro: Ends the song with the greeting he had.