How do you know that the water does not refer to baptism? John said I baptize you with water but one greater than I will baptize you with spirit and with fire.
When we are born of the flesh we are born in Adam’s sin. How could Jesus mean that we must be born in sin and spirit to enter the kingdom of heaven? Sin does not gain us entry
Taking scripture as a whole, it stands to reason that he means that we must be washed in the waters of repentance by dying to self, then renewed to life by the spirit so that we may walk in His ways.
We cannot hold on to our flesh and be ruled by it, while also laying claim to the kingdom of God. Jesus says anyone that saves his life will lose it, but anyone that loses his life for my sake will save it. Paul says when we are baptized in Christ, we are baptized into his death, and he also instructs us to mortify the deeds of the flesh
We are born again when we decide to die with Christ and then we will also be raised with him.
If all we do is sprinkle water on ourselves and claim the name of Jesus, how are we different from the ones that say lord, lord, yet Christ says I never knew you, away from me ye who work iniquity? When we are born again, we give up the desires of the flesh, and live by the spirit. Old things have passed away all things become new