Forms even in the driest regions.
Dew delivers water to plants, insects and small animals even in the driest regions.
Due to its dependence on radiation balance, dew amounts can reach a theoretical maximum of about 0.8 mm per night; measured values, however, rarely exceed 0.5 mm. In most climates of the world, the annual average is too small to compete with rain. In regions with considerable dry seasons, adapted plants like lichen or pine seedlings benefit from dew. Large-scale, natural irrigation without rainfall, such as in the Atacama Desert and Namib desert, however, is mostly attributed to fog water. In the Negev Desert in Israel, dew has been found to account for almost half of the water found in three dominant desert species, Salsola inermis, Artemisia sieberi and Haloxylon scoparium. Another effect of dew is its hydration of fungal substrates and the mycelia of species such as Pleated Inkcaps on lawns and Phytophthora infestans which causes blight on potato plants.
Wikipedia, Dew, 2019
Dew forms even in the driest conditions. However this was portrayed in the Quran 1400 years before it was discovered. The Quran says that if it wasn't rain then it will be dew.
[Quran 2:265] And the parable of those who spend their wealth seeking Allah's approval, and to strengthen their souls, is that of a garden on a high ground. If heavy rain falls on it, its produce is doubled; and if no heavy rain falls then dew. Allah is seeing of everything you do.
If it wasn't rain then it will be dew. Today we know that dew reaches the driest regions on Earth.
How could an illiterate man who lived 1400 years ago have known that rain or dew reach everywhere?
For "garden on a high ground. If heavy rain falls on it" see: Orographic Effect.