Jesus answered, "Most assuredly I tell you, unless one is born of water and spirit, he can't enter into the Kingdom of God!
Born of water is a reference to the ceremony of baptism; but there is no magic in water, nor does the ceremony itself contribute anything to sanctification, as often alleged.  Millions of faithful Christians can testify that submission to the commandment of baptism did not automatically give them a new nature, the new nature coming through a growth process in consequence of the endowment of the Spirit.  Care should be taken to distinguish between "baptism" as a reference to the immersion ceremony, and "baptism" meaning the new birth of which the ceremony is an element.  Jesus himself used the word in this latter sense in  Mark 16:16.