You were expecting to find water ether. What you’re finding is traces of fire ether.
And you ran into a bomb powered by fire ether, didn’t you. Perhaps another one was set off below the drain?
It wouldn’t explain why there’s so much water, though. But maybe the blast sent a lot up at once, and it’s slowed down because there isn’t as much flowing in now?
That’s too complicated for you to say for sure. Is there something simpler?
Well, yes actually. The simplest way for fire ether to explain excess water is if someone brought in a big chunk of ice – such as what was in the kitchen at Patterson’s – and simply melted it.
Then why not just use water ether instead? Summoning a large mass of water is just as easy as producing enough fire to melt ice. You learned both on the first day of your apprenticeship…
So maybe the caster isn’t even an apprentice. It’s someone who’s stumbled onto their power and doesn’t fully understand it yet. They figured out how to make fire, or at least heat, but not how to create water.
Hmm. Well, that all lines up in theory, but you can’t really prove it any more than you can prove it was a bomb. Or something else you haven’t even thought of.
So maybe there’s something else here that could help you narrow down the possibilities.