My 1.25 acre pond is essentially entirely filled with well water.
I would ask other people nearby who've had wells drilled if they could provide a breakdown of alkalinity, pH, hardness, iron content, contaminants, etc.
Also, as D.I.E.D hinted at, it would be nice to know the typical depth at which they find water so you could make some estimates of electrical usage.
Issues like seepage are paramount if you're going to do this. You could also modify the goal and create a 3 acre lake with a maximum depth of 12 feet and an average of 5 feet. This would be 15 acre feet and 3 million gallons. You could manage the heck out of a pond like that and keep costs contained a little bit.
