- 1). Establish the definition of what is considered "hot water." For example, cold water could be measured as anything under 50 degrees Fahrenheit; while hot water can be measured by water temperatures over 85 degrees Fahrenheit.
- 2). Estimate the hot water usage percentage. For example, if you always shower with water exceeding temperatures of 85 degrees, the percentage of hot water usage is 100 percent. If the water knobs are split evenly between cold and hot, the hot water usage is approximately 50 percent.
- 3). Measure the flow speed. The flow speed will be labeled on the box of newer faucets, dishwashers, shower heads and other appliances. If your flow speed is not provided, you can measure how long the water source takes to fill up a one gallon pail. Divide 60 by the time in seconds -- it takes to fill up one gallon -- in order to calculate gallons per minute. For example, if a faucet takes 30 seconds to fill a one gallon container with hot water, the flow speed would be 2 gallons per minute (6 /30 = 2)
- 4). Measure the total time for both hot and cold water usage. For example, if a faucet is used for 40 minutes at a flow rate of 2 gallons per minute, the approximate total water usage is 80 gallons. (40 x 2 = 80)
- 5). Multiply the percentage of only the hot water usage by the total water usage. Make sure the percentage is in decimal form. Convert a percentage b dividing the percentage by 100. For example, if 80 gallons of water was used and the hot water comprises of 70 percent, the hot water consumption is 56 gallons (80 x .70 = 56).
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