This topic has been discussed within a lot of different threads.....maybe mr. ewest or someone can link up to a couple for you.
My experience is that typical groundwater (GW) lacks high dissolved oxygen concentration. depending on where you are in the world, it can have high alkalinity, hardness, low or high pH, but these things can be overcome by getting a water quality test to know if you need to add lime or some other substance to help correct physical chemistry issues (get the pH neutral, etc.), and allowing the GW to run overland (for oxygenation) before entering pond, or aerating as pond is filling.
i'm sure that lots of folks on this forum have a significant volume of their ponds full of well water and do just fine, maybe they can share some of the things they need or dont need to do.
