In 1Pet 3:21 'by' is dia...What's up with that??? Blue Letter Bible
I’ve looked at all of the literal English translations. Only the KJV uses “by” for ‘dia’ for 1 Peter 3:20.
Even the super literal almost mechanical YLT has through for ‘dia.’
YLT:
20 who sometime disbelieved, when once the long-suffering of God did wait, in days of Noah — an ark being preparing — in which few, that is, eight souls, were saved through water;
The LEB which is also a literal translation from LOGOS has this:
LEB:
20 who were formerly disobedient, when the patience of God waited in the days of Noah, while an ark was being constructed, in which a few—that is, eight souls—were rescued through water.