The EDGE software estimates water use in homes by considering elements that contribute to potable water demand, focusing on indoor and occupant-related usage. The EDGE User Guide details the elements included in water use calculations: "In EDGE, water use in homes is estimated based on occupant activities, including water for showers, faucets, toilets, laundry, and water heating, which accounts for hot water demand in these applications. These elements are modeled using standard usage assumptions for residential buildings" (EDGE User Guide, Section 5.2: Water Efficiency Measures). Option B, water heating, is explicitly included, as it represents the hot water demand for showers, faucets, and laundry, which is a significant component of residential water use. Option A (HVAC) is incorrect, as HVAC systems primarily consume energy, not water, except in specific cases like cooling towers, which are not typical in homes: "HVAC systems in homes, such as air conditioners, do not directly contribute to water use in EDGE calculations, unlike in commercial buildings with cooling towers" (EDGE Methodology Report Version 2.0, Section 4.2: Water Savings Calculations). Option C (exterior fountains) is also excluded, as EDGE focuses on indoor water use: "Exterior water use, such as for fountains or irrigation, is not typically included in EDGE’s water use estimates for homes, unless specifically modeled as an optional measure, which fountains are not" (EDGE User Guide, Section 5.3: Additional Water Efficiency Measures). Option D (solar water heaters) is a measure to reduce energy use for water heating, not an element of water use itself: "Solar water heaters reduce the energy demand for water heating but do not change the volume of water used, which is what EDGE estimates for water use in homes" (EDGE User Guide, Section 4.2: Energy Efficiency Measures). The EDGE Methodology Report further specifies: "Water use in homes is calculated based on per-capita assumptions for activities like showering, flushing, and water heating, ensuring a standardized baseline for savings calculations" (EDGE Methodology Report Version 2.0, Section 4.2: Water Savings Calculations). Thus, water heating (Option B) is the element considered in EDGE to estimate water use in homes.