Power from flow and head
The power a pump gives to water is density x g x flow x head. In US farm units that becomes water horsepower = gallons per minute x feet of head / 3960. Divide by the pump and motor efficiency to get the power the motor must draw.
Total dynamic head here is the pumping water level, plus a flat 20 feet for pipe friction, plus 50 psi at the pressure tank (50 x 2.31 = 115.5 feet). That is a simplified sizing estimate; installers use friction tables and the pump's own curve.
Try it: keep 12 gal/min and move the pumping level from 50 to 400 feet. Total head nearly triples, from about 186 to 536 feet, and the input power climbs from about 1 hp to almost 3 hp at 55 percent efficiency.
Why drawdown matters
The resting water table is not where the pump lifts from. While pumping, the level in the well drops by the drawdown, and nearby wells can feel the edge of the cone. Pumping more slowly or for longer, gentler cycles keeps the cone shallower.