This isn't necessarily an easy thing to do, but a landscape architect could help you identify a rough sketch of conventional landscaping for the region, and then your landscaper could help estimate how much water per square foot they would recommend for that type of landscaping. You might also touch base with local water conservation organizations or groups promoting xeriscaping. Keep in mind that Option 2 is open to all buildings but you can’t mix and match the calculations: you can’t develop a theoretical baseline according to Option 2 and then compare that to your metered data for July.