"drinkable, suitable for drinking," early 15c., from Old French potable (14c.) and directly from Late Latin potabilis "drinkable," from Latin potare "to drink" (from PIE root *po(i)- "to drink").

"undrinkable," c.1600, from assimilated form of in- (1) "not" + potable, or else from Late Latin impotabilis.