Dew is the water that condenses on objects that are close to the ground. Due to the fact that dew is caused by the air temperature dropping, it usually can be observed in the early morning hours as this is when temperatures are at their lowest. Aside from the temperature dropping, humidity is another prerequisite for dew forming.

Depending on its temperature, air can absorb water vapor. The warmer the air the more vapor this is. When the maximum absorption has been reached the air is referred to as being saturated. If this dew point is undermined, the water vapor in the air condenses and deposits itself on the ground, on plants close to the ground or other objects. Agriculture welcomes this phenomenon because it results in the
ground being watered in a natural way when there is not enough rain. The air can absorb enough humidity, especially near water bodies so that there is dew. Dew can also develop in the desert and can be one of the few irrigation options without which it would be impossible for plants and animals to survive. In emergencies, when there are the appropriate basins, it can be used as drinking water.

But dew can also develop when a cold object is brought into a warmer room in which there is a relatively high level of humidity. Then the water vapor condenses on the cold object. A good example for this phenomenon is the cold pair of glasses, with which one enters a warm room. If there is sufficient moisture in the air the glasses will condensate immediately.

Dew is never mentioned during the weather report. It is only of relevance for the general public if it is frozen. Then, however, it is referred to as frost. This frost develops like dew, the difference however being that when temperatures are below freezing it does not condense as water but as ice. Then it can become very slick ice in places where it is particularly cold, such as on bridges.

Fog should not be taken for dew. Fog also consists of water droplets that developed as a result of condensation but which do not condense on objects and instead remain in the air. If the fog is very thin one speaks of haze. However, fog dew can also have a moistening effect. In certain areas it is a welcome source of moisture which is caught by some needle wood, such as the Canarian Pine tree which has large
needles that have a particularly large surface.