Why does the law require it be discarded? Simple, because it may have been exposed to biological contaminants, and is therefore deemed "unsafe for consumption". On top of all else, do we really need an epidemic of cholera, or typhus in the area?
the infowarrior
I think the key words here are "may have been". It's required mainly as a CYA thing so they don't get sued to death. If the stuff isn't sitting in the water right now (and it isn't something perishable like diary) it is probably okay. Without electricity a lot of perishables aren't worth anything now either.