Reuse your water.
Water is a precious commodity, and too much of it goes down the drain. Install a rain barrel that attaches to your downspouts and collect rainwater off your roof. Rainwater is relatively free of contaminants and can be used instead of tap water for all kinds of outdoor uses: watering gardens and lawns, cleaning sidewalks and washing the car. Add to the benefit by reusing your gray water -- the waste water from doing dishes, laundry and showering. It's fine for watering plants.
Rain barrels cost $100 to $300 and collect from 50 to 100 gallons of water each. Savings on your water bill will likely be nominal. Recycling gray water can be as simple as reusing the water last night's pasta dinner boiled in to water your plants. More sophisticated systems, such as the Aqus from WaterSaver Technologies, disinfects, stores then and reuses the water from your bathroom sink to flush the toilet. It costs about $200 and reduces wastewater by up to 5,000 gallons per year in a typical household.