Greywater recovery in EDGE is a water efficiency measure, and the software calculates savings by comparing water consumption before and after implementing the measure. The EDGE Methodology Report explains the calculation method: "Water consumption savings from greywater recovery are calculated as the difference between the Base Case water consumption and the Improved Case water consumption after applying the measure. The Base Case represents the typical water use without any efficiency measures, serving as the benchmark for all savings calculations" (EDGE Methodology Report Version 2.0, Section 4.2: Water Savings Calculations). Option A, Base Case water consumption, is the correct reference point for determining savings, as it establishes the baseline against which the greywater recovery measure is evaluated. Option B (Improved Case water consumption) is the result after applying the measure, not the basis for savings. Option C (cost of water consumption at local tariff) and Option D (incremental cost of installation and cost of water consumption at local tariff) relate to financial outputs, not the direct calculation of water savings, as clarified: "Water savings in EDGE are quantified in volume (liters or cubic meters), not cost, though cost savings are derived later using local tariffs" (EDGE User Guide, Section 5.2: Water Efficiency Measures). Thus, greywater recovery savings are based on Base Case water consumption (Option A).