I don't even think early Christians called themselves "Christian".
Probably not but I'm also sure that teabaggers didn't call themselves "The Tea Party" until fairly recently while still holding the same beliefs. Having a label come later doesn't mean it's wrong.
Most church names (e.g., "Church of Christ") don't use that term either.
That's because they worship Christ, not Christians you putz.
It's a diluted term preferred more by atheists.
Actually I prefer the term "Deluded Supernaturalist Worshipers of Zombie Jesus".
Ditto for the secularization of the term "flood", which is obviously reminiscent of the Great Flood.
Right, because no smaller scale floods have ever existed for the entirety of Earth's history. Nope, there was only one flood ever.
"Flood-waters" is a particularly silly secularization
Flood-waters is a descriptor of the type of waters meaning they come from a flood as opposed to other sources. It's a term describing the waters rather than than the flood itself. The words aren't even equivalent so how can they be counterparts to each other?
does anyone think it might be anything other than water in natural disasters?
Earthquakes, dust devils (Oh noes, I said devils!), landslides, and volcanic eruptions. None of these have water as an essential component. Hell, if one is being generous in the use of the term "flood" it doesn't even necessarily have to involve water either as people can say that, for example, the streets are flooded with garbage or Conservapedia is flooded with bullshit.