If the water is not fully draining from the dishwasher, try these troubleshooting steps to determine the potential cause.
First, find the dishwasher drain hose. As dishwashers are typically beside the sink, look in the cabinet underneath the kitchen sink. If the hose is installed at the bottom of the cabinet, excess sink water may backflow from the garbage disposal (if installed) into the dishwasher. The hose may need to be removed and installed higher up to prevent water backup.
Next, an air gap may be installed above the rim of the sink. This connects the hose from the dishwasher to the garbage disposal and helps prevent the contaminated water from re-entering the dishwasher. However this air gap valve or hose can get clogged, which will cause water backup. You will likely notice a smell of standing water if this is clogged. The air gap will need to be cleared to allow the water to flow as designed.
Finally, a check valve may be installed to allow water to flow in one direct but will prevent the dirty water from re-entering the hose. However this may be damaged or locked in the open flow position, allowing water to flow both ways. This valve will need to be reinstalled, which may require the connected hose/pipe to be replaced as well. If reinstalling the hose, be sure to position the hose to move up (preferably into the sink cavity) and back down to the garbage disposal to allow the water to flow properly. Check out the video below for further details and visual information.