The word "baptism" or "baptize" is not even mentioned by Christ. Jesus was speaking to one of the sandredrin, one versed in the ceremonial use of water throughout the clean and unclean PURFICATION laws of Israel which was a symbol of the Spirit of God as Jesus demonstrates in His own use in his very next conversation about water and salvation in the very next chapter:
10 Jesus answered and said unto her, If thou knewest the gift of God, and who it is that saith to thee, Give me to drink; thou wouldest have asked of him, and he would have given thee living water.
11 The woman saith unto him, Sir, thou hast nothing to draw with, and the well is deep: from whence then hast thou that living water?
12 Art thou greater than our father Jacob, which gave us the well, and drank thereof himself, and his children, and his cattle?
13 Jesus answered and said unto her, Whosoever drinketh of this water shall thirst again:
14 But whosoever drinketh of the water that I shall give him shall never thirst; but the water that I shall give him shall be in him a well of water springing up into everlasting life.
Indeed, right after Jesus finishes speaking to Nicodemus the disciples of John got in a dispute with the Jews over the ceremonial rites of purification:
Jn. 3:25 Then there arose a question between some of John’s disciples and the Jews about purifying.
Paul makes it clear that baptism has nothing to do with literally saving anyone or with regneration or the power of God to save:
1 Cor. 1:17 ¶ For Christ sent me not to baptize, but to preach the gospel: not with wisdom of words, lest the cross of Christ should be made of none effect.
18 For the preaching of the cross is to them that perish foolishness; but unto us which are saved it is the power of God.
you just said the same thing as me in different words... =)