Not to be difficult here, but according to Robyn at Metalico Granite City (Lawrence brand chilled shot) the purpose of the inorganic arsenic additive is not to harden, but to reduce the surface tension of the molten lead mixture. It has the same affect on lead as soap does on water.
The reason they add the inorganic arsenic is so when they make the chilled shot, the melt forms into nice round balls. Otherwise the process would just make ugly little globs. This roundness is what helps them fly straighter and truer when fired in your shotgun.
The anitmony added is what hardens the lead. The "high antimony" is about 5% while the standard chilled shot is only 2%. You can ask her about the hardening effect of the water, but if I recall, it is negligible.
Please read a little bit about the shot at the link I've attached. Call and talk to Robyn about getting the material safety data sheet (MSDS). She will help you with any questions about the content of their products, as well as the process by which the shot is made. This is a good source of antimony in that is is very repeatable and uniform.
http://www.maycoindustries.com/shot.htm