Dishwashers DO need hot water.

In order for the dishwasher to melt grease and the dishwasher detergent to dissolve, dishwashers require a water temperature of at least 140°F.

Save Money by Purchasing the Right Dishwasher

Though they cost more initially, purchasing a dishwasher with a booster heater will generally pay for itself within the first year.  A dishwasher with a booster heater will raise the temperature of the water running through the dishwasher allowing you to set the water temperature running throughout the house to a lower setting.

How to Lower Your Dishwasher Usage Costs

Run only full loads.  If you are using an Energy Star® rated dishwasher and only fun full loads, you will actually save money over hand washing the same load of dishes.

Purchase a dishwasher that offers a variety of cycle setting that can accommodate both small and large loads.  Small capacity dishwashers don't always save money.  Though it's true that running a smaller dishwasher is more energy efficient than running a larger one, if you need to run it more than once it is likely costing you more. 

Choose a dishwasher model that offers energy saving options such as an air dry cycle and shorter cycles for fewer dishes.

Install your dishwasher in a location that is not abutting the refrigerator.  The heat and moisture produced by the dishwasher makes your refrigerator have to work harder.