In recent years, the cost of water usage has increased signi‘cantly and represents an important portion of the total utility bills, especially for residential buildings. In some western U.S. cities where the population growth has been high, the cost of water has increased by more than 400% during the past 10 years. In the future, it is expected that the cost of water will increase at higher rates than the cost of energy. In the United States, energy used for domestic hot water accounts for 15% of residential energy consumption, the third largest energy end use in homes a¬er space heating (47%) and lighting and appliances (24%), as indicated by a survey conducted for residential energy consumption (EIA, 2009). ˜erefore, it is worthwhile to explore potential savings in water use and water heating expenditures during a building energy audit.