How to Fix Sitting Water in Dishwashers. A dishwasher's drainage basket and sump blocked with food particles is the most common cause of water remaining at the bottom of the unit. Standing water at the bottom of a dishwasher or complaints that a dishwasher won't drain are fairly common issues. While there are multiple reasons why water won't drain completely, or will seep back into the dishwasher, most of them do not warrant a call to the appliance repairman.