It’s a common view that the ark saved Noah and his family from the water. The flood is seen as the threat to their safety, since it destroys the human population of that period.
That view is reflected in what must be the worst rendering of the New Living Translation, which I otherwise appreciate: “Only eight people were saved from drowning in that terrible flood” (1 Peter 3:20). The original text says nothing about drowning!
The literal rendering of the last part of this verse would be close to the KJV: “wherein few, that is, eight souls were saved by water.” The New Century Version also is close: “Only a few people—eight in all—were saved by water.”
The Greek term for the preposition “through” or “by” is dia. Its range of meanings includes the spacial and temporal, as well as indicating the agency or means. Peter’s comparison of the water of the flood with baptism requires that the water be considered, not the threat or danger, but the means by which Noah was saved.
But from what was he saved? The text is not explicit, as it is not explicit from what baptism saves, but for what it saves, that appeal for a good conscience before God. (Peter’s use of “save” and “salvation” in 1 Peter does not reference salvation from anything.)
If we had to risk a guess, we’d say that the flood waters saved Noah from the wicked generation, from that “ungodly world” (2 Peter 2:5) to which he preached as he built the ark.
Be that as it may, a number of Bible versions clearly show the preposition to be used in the sense of agency or means.
When the NIrV wanted to communicate clearly, here’s how it translated 1 Peter 3:20: “A total of eight were saved by means of water.” As noted above, the KJV also translates it as “by,” which is clearer than the fallback and ambiguous “through.”
A number of Portuguese versions also bring out the idea of means: NVI, BJ (por meio da água), TEB, VFL (pela água).
The Lutheran Study Bible (Concordia, 2009) brings out the sense of the passage: “The flood is a figure of Baptism. In each case, water saves. The world was cleansed when Noah and his family were lifted up by the flood. Baptism cleanses and raises us to new life.”
The water of the flood saved Noah and his family. In a similar fashion what saves us today (“now”) is baptism. There is no special water, no efficacy in the water itself, other than as an act of faith to obey the word of God and trust that his promise of cleansing from sin occurs in that act.