The knowledge that the blood of Jesus Christ saves is meaningless without the understanding of how to come in contact with it. Knowing something exist does not grant the reward of its existence. Proclaiming "only the blood saves" has no effect on the salvation of anyone, it is the response to His gospel that saves.
Proclaiming "penicillin cures staph" is true but is useless without the proper administering of the medicine. Those who proclaim the cure but deny the proper administering of the cure are leading many to their doom.
All the blood on every door post in Egypt would not save without the first born safely under its shadow. Any first born not obedient to this command died. The blood only saved the obedient.
You state, "Water cannot save." If God chooses, it most certainly can.
Baptism, which is like that water now saves you. (1 Peter 3:21a)
Who are we to debate Him?
We aren't to debate Him, but we can certainly debate you, and your understanding of 1 Pet 3:21.
(NIV) and this water symbolizes baptism that now saves you also--not the removal of dirt from the body but the pledge of a good conscience toward God. It saves you by the resurrection of Jesus Christ,
Noah was saved through water, which symbolized the baptism that now saves us, which is baptism in the Holy Spirit.
1 Cor 12:
13) For
by one Spirit are we all baptized into one body, whether we be Jews or Gentiles, whether we be bond or free; and have been all made to drink into one Spirit.
Acts 1:
5) For John truly baptized with water; but ye shall be baptized with the Holy Ghost not many days hence.
Mat 3:11)
I indeed baptize you with water unto repentance:
but he that cometh after me is mightier than I, whose shoes I am not worthy to bear:
he shall baptize you with the Holy Ghost, and with fire:
Luke 3:16) John answered, saying unto them all,
I indeed baptize you with water;
but one mightier than I cometh, the latchet of whose shoes I am not worthy to unloose:
he shall baptize you with the Holy Ghost and with fire:
Eph 4:
5) One Lord, one faith,
one baptism,
Eph 1:
13) In whom ye also trusted,
after that ye heard the word of truth, the gospel of your salvation: in whom also
after that ye believed, ye were sealed with that holy Spirit of promise,
14) Which is the earnest of our inheritance until the redemption of the purchased possession, unto the praise of his glory.