I am in research stage of converting from propane heat to geothermal. I aim looking to maximize efficiencies as much as possible. For example during the cooling cycle I wish to reclaim heat for our swimming pool. I have researching the merits of each type of setup, open loop appears to be more efficient. I don't want to wastefully discharge ground water, so could I have the system supply domestic water, fill a cistern, and use it for irrigation? What is left over would go into a return well. Would this set up be more efficient than running my conventional well pump.

I don't understand the difference between what you propose vs "running my conventional well pump" Regardless of what you do with the open loop water, you initially have to get it out of the ground.

No need to have a cistern to accumulate open loop discharge water for irrigation - a small artificial pond may be cheaper to construct.

I pass my 92 degree open loop discharge water through a 600 gallon Intek pool, and it is very popular with my kids all summer. On my to-do list is to contain and distribute that water for irrigation.

I firmly believe that in most climates north of I-10 most if not all rejected heat could be contained in and dissipated from a conventional in ground pool, possibly via the addition of a fountain running at night if pool temps became too high, but I have yet to test this hypothesis. Such a pool might even serve as sole source for winter heating in the mid to deep south, though it wouldn't be a popular place to swim from November through March

Curts first comment about getting water out of the ground is something you might miss. Op cost projections do not include cost of runnin a well pump. Therefore you might want to research closed loop as well.
good luck,
joe