The water is symbolic of a "cleansing" process. As scripture says, we are saved through water just like Noah was. With Noah, water killed the sinful men, buried them. With baptism, water buries the dead "old man", and the new man is resurrected .... as Jesus died, was buried, and resurrected. There is nothing magic about water, but it is symbolic in so many ways... and the bottom line is, we were told to do it.... we don't have to understand exactly why, like Naaman.... just do it. God commands it. Repent, and be baptized... the act of baptism is an appeal to God for a clear conscience, through Jesus' resurrection.