Make it a full load! Run your dishwasher only when it’s full. Don’t pre-rinse dishes – tests show pre-rinsing doesn’t improve dishwasher cleaning, and you’ll save as much as 20 gallons of water per load. When you buy a new dishwasher, look for one that saves water. Water-efficient models use only about only about 4 gallons per wash.
A dishwasher can be a great water and energy saving tool, if used effectively.
Fill the dishwasher completely before operating. Partial loads waste electricity and water. Proper loading is important for the dishwasher to work efficiently.
Short wash cycles, rinse-only cycles, mid-cycle turn-off, and other features are designed for energy conservation as well as convenience. Connect your dishwasher to cold water supply unless otherwise directed. Normally only one wash and one final rinse cycle requires hot water which is heated by an element in the dishwasher.
Keep your dishwasher filters free of debris. A blocked filter reduces efficiency and wastes energy.
Source: the Enviropaedia