There are a few reasons why your dishwasher might be leaving spots on your dishes. One possibility is that your water is not hot enough. Dishwashers typically require water that is at least 120 degrees Fahrenheit in order to effectively clean dishes. Another possibility is that your dishwasher is not draining properly, which can cause dirty water to be re-circulated onto your dishes. Finally, it is also possible that your dishwasher needs to be descaled. Over time, hard water can leave mineral deposits on the dishwasher components, which can then be transferred to your dishes.