The answer or conditions for salvation must be something that all can give or do. Therefore we must reject all claims that the Bible has been corrupted, or that books have been removed or lost, or even, that it isn't complete or no longer relevant to our generation. To contend that the Bible is not an infallible and complete guide, is to contend that there exists no answer to the above question. Actually, the passage is teaching that baptism is included in the process by which one is made a disciple. One can't enter the Kingdom of God until they are born of both water and the spirit.
Baptism is part of the process of being born again.
Thus beware when someone tries to sell you on the idea of an easy and convenient relationship with God, avenue to heaven, or a way in which you can be saved and yet still live the life that you selfishly want to live. Be impressed that Jesus expected the same standard of dedication from all who would follow Him. It seems that today some assume that one can be far less committed to Christ than the apostles or the early Christians and yet still end up saved. An honest person cannot read Hebrews chapter 11 and walk away thinking that the faith that saves is the mere mental acceptance that God exists or that Jesus is the Son of God. In the book of Acts God has given us a record of what people did to become Christians.