Question: Out of all the raw materials that can possibly be used in a 3D Printer, are any of them water soluble? As in, they will dissolve in water?
PVA is the only one i know of - Lulzbot carries small spools of the stuff.
If you’re not limited in scope to just filament-based 3D printers, molten sugar is an option.
I’ve also seen salt used. I believe it was a powder/binder process, but it might have been SLS.
There have been extruder based prints using porcelain clay and chocolate, so cold porcelain clay, which is water soluble, might be printable as well. I wasn’t able to find anything on the solubility of porcelain clay, nor whether porcelain clay and cold porcelain clay are related.
HIPS (High Impact Polystyrene) has also been used:
Basically, PVA is temperature compatible with PLA, and HIPS is temp compatible with ABS.