Water baptism is not required to be saved, this is proven in Scripture when Jesus was being crucified, there were two men with him, one got saved right there before he died, he had no way of getting baptized.
Water baptism certainly does not give evidence that one is saved, I know this because I was baptized before I got saved and all that did was get me wet, all Scripture shows they got baptized after they were saved.
Water baptism is a public profession of faith saying that you believe that Jesus is the only One saving you.
Water baptism is following Jesus' command of the great commission.
Water baptism is following Jesus, who got baptized, we are to be followers of Christ.
Water baptism is fully accepting the Holy Spirit that is in you, most of the people we learn about in the Bible only received the Holy Spirit or at least
acknowledged that He was in them when they got baptized.
Spiritual baptism is need to be saved, which is received when we receive Christ as our Savior.
All these things I mentioned can be backed up with Scripture.