My basement flooded due to faulty washer, and my dehumidifier was standing in about 3 inches of water. Is it safe to use this dehumidifier?

Hard to say without knowing what components are in that space. However, move it to a dry space, use a hairdryer to dry off as much water as possible and then plug it in. It won't blow up. It may trip the breaker, not run or work fine.