Hey Joe
Here in E NE we receive 29" of precipitation annually - and using that formula the NRCS stated it requires 33 acres of watershed to naturally sustain water levels for a 1 acre pond.
My watershed is just over 40 acres. I built a 4 acre pond. I irrigate to supplement precipitation. For me the cost of drilling a well was worth it as I plan to live there someday. Hope this is helpful.