An automatic dishwasher fills up with water even when there are no dishes inside because it follows a predetermined cycle that includes multiple stages, regardless of whether there are dishes to wash or not. Here's a general explanation of the dishwasher cycle:
Pre-wash/rinse: At the beginning of the cycle, the dishwasher typically performs a pre-wash or rinse to remove any loose food particles or debris from the dishwasher itself. This helps ensure cleaner washing results.
Main wash: After the pre-wash, the dishwasher enters the main wash stage. It fills up with water from the water supply, and the detergent is released into the dishwasher. The water is heated to the desired temperature, usually between 120 to 140 degrees Fahrenheit (49 to 60 degrees Celsius), to aid in effective cleaning.
Spray and agitation: During the main wash stage, the dishwasher's spray arms rotate and spray high-pressure water jets throughout the dishwasher. These jets help dislodge and remove food particles and stains from the dishwasher's interior, including the walls, racks, and filters.
Drain and rinse: Once the main wash is complete, the dishwasher drains out the dirty water. It then fills up with clean water for a rinse cycle to remove any remaining detergent or debris.
Final drain: After the rinse, the dishwasher drains out the clean water, leaving the dishwasher interior free of water.
The dishwasher goes through these stages regardless of whether there are dishes inside. This is to ensure that the dishwasher remains clean and ready for its next use. If you don't have any dishes to wash, it's still a good practice to occasionally run an empty cycle to keep the dishwasher clean and maintain its optimal performance.