Switch to a low flow showerhead. Choose one that "aerates the water" and you can keep up the pressure while halving water use
Using less water in the shower saves you the expense of heating it while also helping stave off drought, a serious problem, particularly in the American Southwest and Southeast. Aerators mix air into the water stream, maintaining water pressure while using less water. Water-saving non-aerating showerheads flow in pulses, creating a massage effect. These showerheads can reduce the flow from 2.5 gallons per minute (gpm) to less than 1 gpm, saving 15 gallons of water on a ten-minute shower. Many utilities will either provide low-flow showerheads free of charge or offer rebates on store purchases. For more, see NRDC's Simple Steps.