God saved Noah. The fact is Noah was saved FROM the water and not by the water. That is a fact. It is the water that killed everyone. You are only looking at half of the equation.
Water symbolizes both life and death in hte Bible.
That is what Peter is saying. Just read the text and not read into it. In the spiritual sence, seperation from God. And the death he was spared from was drowning. Noah was saved from death by via water and a boat.