A dishwasher can fill with water even when it's not running due to a few possible reasons:
Air Gap or Drain Loop: Dishwashers are usually connected to the kitchen sink's drainage system through either an air gap or a drain loop. The air gap is a separate device mounted on the sink or countertop, while a drain loop is a hose arrangement. Both of these prevent dirty water from the sink from flowing back into the dishwasher. Sometimes, water may flow from the sink into the dishwasher through these connections if there's a partial blockage or a siphoning effect.
Sink Clogs: If the sink's drain is clogged or partially blocked, water can back up into the dishwasher through the shared drainage system.
Faulty Water Inlet Valve: The dishwasher's water inlet valve is responsible for allowing water to flow into the dishwasher when needed during a wash cycle. If the valve is malfunctioning or has a faulty seal, water might slowly leak into the dishwasher even when it's not in use.
Drain Hose Placement: If the dishwasher's drain hose is not properly positioned or secured, it might allow water to flow back into the dishwasher due to gravity or other factors.
Plumbing Issues: There could be issues in the overall plumbing system, such as improper venting or a lack of check valves, which can lead to water flowing back into the dishwasher.
If you notice water entering your dishwasher when it's not running, it's important to investigate the cause and address it promptly to prevent any damage to the dishwasher or surrounding areas. If you're unsure about how to troubleshoot or fix the issue, it's best to seek the help of a professional plumber or appliance repair technician. They can identify the problem accurately and ensure it's resolved correctly.