Could be the Mothers' waters ' ( born of flesh ) A jew believed his ethnicity was enough , but they had to also be born of the Spirit not just of flesh.
1 There was a man of the Pharisees, named Nicodemus, a ruler of the Jews:
2 The same came to Jesus by night, and said unto him, Rabbi, we know that thou art a teacher come from God: for no man can do these miracles that thou doest, except God be with him.
3 Jesus answered and said unto him, Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God.
4 Nicodemus saith unto him, How can a man be born when he is old? can he enter the second time into his mother's womb, and be born?
5 Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God.
6 That which is born of the flesh is flesh; and that which is born of the Spirit is spirit.
7 Marvel not that I said unto thee, Ye must be born again.
8 The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit.
9 Nicodemus answered and said unto him, How can these things be?
10 Jesus answered and said unto him, Art thou a master of Israel, and knowest not these things?
Nope not born of flesh from the mother, Christ said that which is born of the flesh is flesh, and we know the flesh is corrupt and fallen and has no place in God's kingdom, This is why we will be given new bodies upon the reresection. Therefore an earthly birth does not qualify.
So what could water be? Maybe it has to do with the previous 2 chapters?