Using a dishwasher is one of the most water- and energy-efficient (and easy!) ways to get your dishes, utensils and cups sparkling clean. But there's a good reason not to pre-rinse your dishes: In addition to water waste, modern dishwashing machines are designed to work harder when they detect grease, grime and food particles. If the bottom rack is too clean, your machine will assume its job is done and not wash your dirty top rack dishes properly. Plus, modern-day dishwashing detergent is activated by grease; it won't work properly if your plates are too clean.