[The Dark Mudokon]

Well, the oceans and lakes practically refill themselves 'cuz rain is evaporated water from lakes and ocean that condense and falls back unto the land. :P

And as a natural ecosystem, Oddworld should have the same cycle as the earth so it can suffice itself. So, I wouldn't find it logical that there always chamans that have to make rain fall on Oddworld, in that case, how would chamans exist in the Oddworld Stone Age? Chaman stuff wouldn't be in native mentality.....