Somewhere along the line I mistyped “reservoir” as reservoid, which seems like a fortunate coinage. I'm not sure just what reservoids are, but I imagine some sort of extradimensional storage space. Perhaps in the Harry Potter world it's a trademark for a Bag of Holding? Except no, in that world they have an Undetectable Extension Charm and anyone can cast it, say on a horn filled with seawater.
Google search produces a mix of obvious typos and interesting leads that, on investigation, turn out to be typos. For example, the top hit is about special firewood-storage shelves for next to your fireplace, whose name is actually the totally unimaginative “reservoirs”. A reference to Quentin Tarantino's lost masterpiece Reservoid Dogs is similarly a simple error.
Hit #6 is the Wikipedia article for reservoir sampling, which I took as Google just being a its creepy stalker self.
Hit #8 is from a 1912 Kentucky regulation about slaughterhouse construction.
I also tried searching the database of U.S. trademarks; nobody has trademarked “reservoid”. The term is wide open for anyone who wants to use it.