In a hot and dry climate with low rainfall, water efficiency measures in EDGE are evaluated based on their potential to reduce potable water demand, but their effectiveness depends on local conditions. The EDGE User Guide explains the impact of various water-saving measures: "In regions with low rainfall, rainwater harvesting provides minimal water savings due to limited precipitation, whereas measures like low-flow showers, dual flush toilets, and black water recycling can achieve consistent savings by reducing direct water use or reusing wastewater" (EDGE User Guide, Section 5.2: Water Efficiency Measures). Option B, rainwater harvesting, relies on rainfall to collect water for non-potable uses, but in a hot and dry climate with low water availability, its effectiveness is limited: "Rainwater harvesting systems in EDGE are modeled based on local precipitation data. In arid climates with annual rainfall below 200 mm, savings from rainwater harvesting are typically less than 5% of total water demand, as the collected volume is insufficient to meet significant needs" (EDGE Methodology Report Version 2.0, Section 4.2: Water Savings Calculations). In contrast, Option A (low-flow showers) reduces water use directly: "Low-flow showers can reduce water consumption by 20-30% in buildings, regardless of climate, by limiting flow rates to 6-8 liters per minute" (EDGE User Guide, Section 5.2: Water Efficiency Measures). Option C (recycle black water) also offers consistent savings: "Black water recycling systems can save 30-40% of water demand by treating and reusing wastewater for flushing or irrigation, independent of rainfall" (EDGE Methodology Report Version 2.0, Section 4.2: Water Savings Calculations). Option D (dual flush for water closets) similarly provides reliable savings: "Dual flush toilets reduce water use by 25-35% by offering a low-flush option for liquid waste, effective in all climates" (EDGE User Guide, Section 5.2: Water Efficiency Measures). Given the low rainfall in a hot and dry climate, rainwater harvesting (Option B) yields the lowest water savings compared to the other measures, which do not depend on precipitation. The EDGE User Guide further notes: "In dry climates, measures like rainwater harvesting are often the least effective, while demand-side measures (e.g., low-flow fixtures) and recycling systems provide higher and more consistent water savings" (EDGE User Guide, Section 5.3: Additional Water Efficiency Measures). Thus, rainwater harvesting (Option B) gives the lowest water savings in this context.
[Reference:EDGE User Guide Version 2.1, Section 5.2: Water Efficiency Measures, Section 5.3: Additional Water Efficiency Measures; EDGE Methodology Report Version 2.0, Section 4.2: Water Savings Calculations., ]
