Thank you.
Water is symbolic of the Holy Spirit. Water baptism is symbolic of the baptism of the Holy Spirit each believer undergoes when he is saved.
It is a statement to the world by the believer of his commitment to Jesus Christ and the indwelling of the Holy Spirit as a result of that commitment.
And to underscore that point:
He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water. (But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet [given]; because that Jesus was not yet glorified.) - John 7:38-39