In this optional lesson, students use ratios and rates to work with large numbers and decimals in an environmental context. Students begin by comparing the water flow of different showers to see which shower uses the most water. Then students examine different sources of power to determine how much energy came from each source and how long a fan and an air conditioner were used. Students reason abstractly and quantitatively when deciding to use a tape diagram, double number line, or other technique to approach these problems (MP2).