“Can master zones share resources?” — well, this depends on whether you mean mechanically, or software-wise? To have all four water sources available to all emitters, obviously the water pipes / tubes needs to be connected in some way, and this is not something software alone can control. If you are referring to software, it can be programmed any way you want (for example, you can turn on any combination of any master station and any zone), I don’t think there is any limit on this.