The amount of ag lime needed to raise your soil to its target pH — driven by reserve acidity and your lime's ECCE, not by water pH alone.
Your lime requirement answers 'how much lime per acre?' It depends on three things: your soil's reserve acidity (from the buffer pH or exchangeable acidity), the target pH for your crop, and the ECCE of the material you'll spread.
Water pH alone can't give it to you — two soils at pH 5.8 can need very different lime rates. And it's genuinely state-specific: each land-grant lab publishes its own buffer and calibration table. Some states (the alkaline West) rarely need lime at all.
Related: Buffer pH · ECCE & CCE · Lime by state