Water baptism is not associated with salvation of the spirit.  Water baptism is associated with salvation of the soul.  The thief on the cross did not receive water baptism.  

Water baptism is the first act of obedience after one is saved.  Is water baptism necessary for rewards at the Judgment Seat of Christ?  

Will all those who have a saved soul also have received water baptism?  Salvation of the soul is mentioned three times in the New Testament – Peter, Hebrews, and James. 

There are several books pertaining to the salvation of the soul.  Arlen Chitwood is one author, and Gary Whipple is another.  Govett had some of the first modern day writings on this in the 1800s.