Dew
These objects cool in the night. When they cool, the thin layer of air around them cools too. This makes some water vapor condense on the object. The condensation happens because the air is able to hold less water when it is cooled. The temperature when condensation begins is called the 'dew point'. Most people agree that the water in the dew comes from the atmosphere. However, some studies suggest that it also comes up through the soil and then condenses on the ground. This happens, though, only when conditions are right.