Even if, during your hotel stay, you're turning off lights and lowering the A/C , you may be doing harm simply by giving your business to a place that burns through energy, pollutes water, or produces tons of waste. To ensure that the property you're giving money to is environmentally responsible, look for certification. If it's LEED-certified (there are less than 100 LEED hotels in the U.S., though more are coming), Energy Star-compliant, or sports the Green Seal, you can be more sure that the hotel's eco-commitment is real.