Does ur dishwasher drain to a garbage disposal? Is there an airgap device between drain and dishwasher? If no airgap device, then I would check and see if drain hose is at high point at disposal/drain. If it is, water may be draining into dishwasher from dispoasal/drain/sink. Route drain hose so it is higher than disposal at some point between bottom of dishwasher and where it drains to.

I just moved into a house and the dishwasher had water in the bottom. I found the drain and cleaned it then ran the dishwasher. When it finished running there was no water left in the dishwasher, but a few days later there's water again & the dishwasher hasn't been run again. I'm wondering if the dishwasher needs maintenance/replacement or if there is a problem with the plumbing between the sink and dishwasher??