Most dishwahers don't allow you to choose a "half-full" cycle option.  The dishwasher is either running or it's not.  And if it's running, it's using energy and using water.  So, why not make the most of it and run the dishwasher only when it is completely full?

When purchasing a new dishwasher, choose a model that is Energy Star certified.  Energy Star dishwashers use at least 41% less energy and much less water than conventional models.

A typical dishwasher uses between 8 and 15 gallons of water per load.  A high efficiency dishwasher uses between 5 and 7 gallons per load. 

<<I have an email out to EPA about commercial models and current use versus proposed new standards, which just went into effect 10/07>>