I am working on a model for a large retail space, and need to determine the hot water usage. Based on square footage, FTE and flow/flush rates, I can determine the total water usage (obviously that's WEp1). From that, how do I derive the hot water usage? Is there a standard percentage of hot water out of total water? Does this percentage change based on different space types (for example, I assume that due to showers, residential HW% would be much higher than retail or commercial)? Thanks to anyone who can help me with this.