The tricks with water are for it to be hot and distilled. I first learned about the hot part from a knife care instruction booklet maybe fifty years ago. Take a piece of plain or carbon steel and polish it and degrease it with solvent and boil it in water till it is at boiling temperature through and through. Take a pair of tongs and get them hot in the boiling water before pulling the work out and flicking it to throw loose droplets off. Watch the remaining water evaporate, then, when it is cool enough to handle, take a close look at it under sunlight at several angles and you will see a very thin layer of blue oxide has formed. This is just like boiling things in rust bluing to convert red rust to blue, except the "rust" is forming and bluing as the piece dries. That thin blue layer is protective.
I take advantage of this during Parkerizing. I rinse the part in tap water to get the solution out of it, then boil it in distilled water. That removes any minerals left by the tap water and it converts any oxidized free iron to blue oxide and protects the piece until I drop it into water displacing oil as the final treatment. I do this because I know the military procedure handled the free iron by putting the Parkerized parts into a mild chromic acid solution to coat free iron with chromium oxide so it couldn't rust. I don't want to mess with a chemical that hazardous and hard to legally dispose of, so boiling in distilled water gets the nod. I've never had any after-rust result.
The concern about water getting trapped in threads is real, though. Either a water displacing oil (and WD-40 is one, though I like to remove it with mineral spirits after it has got the water to prevent the surface becoming sticky when it dries), or, since I have an electric annealing oven, I stick parts in there at about 220°F and just let any stuck water be driven out as vapor.
I take advantage of this during Parkerizing. I rinse the part in tap water to get the solution out of it, then boil it in distilled water. That removes any minerals left by the tap water and it converts any oxidized free iron to blue oxide and protects the piece until I drop it into water displacing oil as the final treatment. I do this because I know the military procedure handled the free iron by putting the Parkerized parts into a mild chromic acid solution to coat free iron with chromium oxide so it couldn't rust. I don't want to mess with a chemical that hazardous and hard to legally dispose of, so boiling in distilled water gets the nod. I've never had any after-rust result.
The concern about water getting trapped in threads is real, though. Either a water displacing oil (and WD-40 is one, though I like to remove it with mineral spirits after it has got the water to prevent the surface becoming sticky when it dries), or, since I have an electric annealing oven, I stick parts in there at about 220°F and just let any stuck water be driven out as vapor.