1 Peter 3:20-21
20 Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water.
21 The like figure whereunto even baptism doth also now save us (not the putting away of the filth of the flesh, but the answer of a good conscience toward God,) by the resurrection of Jesus Christ:
Above is a common prooftext for Baptismal Regeneration, which teaches that water baptism is necessary for Salvation. Such see verse 20's mention of "8 souls being saved" as a reference to Eternal Life, and also see verse 21's mention of "baptism doth also now save us" to be in reference to eternal Salvation.
1 Peter 3:20, when discussing Noah and his family, says that "8 souls were saved by water". In the account, Noah and his family's lives are saved from physical death by avoiding the judgment of the Flood.
It's a error to read "soul" here, and think "eternal Salvation". The word "soul" in 1 Peter 3:20 means "life", as is frequently the case in Scripture (Genesis 12:5, 12:13, Joshua 10:35, 39, Job 12:10, Jeremiah 2:34, Lamentations 1:19, Ezekiel 7:19, 13:18-20, Luke 12:20, 21:19, Acts 3:23, 7:14, 27:37, Revelation 16:3, 18:13, etc.). Most modern versions of the Bible render "souls" as "persons" or "people".
In 1 Peter 3:21, Peter says that corresponding to how Noah and his family were saved in the Ark, baptism now saves us. Noah and his family were not granted Eternal Life, nor the New Birth, by being in the Ark. As mentioned above, they were saved from temporal judgment. And what does Peter say in this passage? It's the same way for us.
In what way? Well, water baptism is ordinarily the first step in obedience after Salvation, as we read in the accounts of Pentecost (Acts 2:41), the Ethiopian eunuch (Acts 8:35-38), and the Philippian jailer (Acts 16:30-33). It's a command from the Lord to all converts (Matthew 28:19).
Therefore, in fulfilling the command as a new convert, water baptism gives us - as the passage in question states - "the answer of a good conscious toward God", as the first step in obedience as a Christian. As with any commandment, if you fail to obey, God is liable to chasten you (Hebrews 12:6, etc.). Fulfilling the command saves you from that chastening.
Water baptism also serves to, as in Noah's generation, call you out from among the world (2 Corinthians 6:17). It is a public symbol of your spiritual baptism that you received when you believed (Ephesians 1:12-14), and a symbol that pictures the new birth that you received by faith, prior to water baptism (John 1:12, Galatians 3:26: 1 John 5:1). It publicly identifies you as a Christian.
It is a grave mistake, however, to place more emphasis on the symbol, than on the spiritual truths that the symbol was designed to represent, which are not contingent on being water baptized, but instead are contingent on believing in Jesus.
Those on the Ark were saved from God's temporal wrath here on this earth, and from the wickedness of those who had corrupted the earth - and Peter likens water baptism to that salvation. Salvation from Hell is foreign to the passage.