What is dew?

The damp and delicate dawn visitor – where does it come from?

Magically, silently, while we sleep through a clear, still night, every blade of grass, every car windscreen, every garden table and chair become coated in millions of minute droplets of fresh water.

Dew - Mother Nature’s most delicate of face-washes – is such a familiar sight first thing in the morning, at any time of year, that we take it for granted, perhaps without questioning how or why it forms – and out of a cloudless sky too.

Mother Nature’s most delicate of face-washes

But does dew fall from the sky or rise from the ground? Well actually neither. All air contains water. Much of the time it’s an invisible vapour, but it’s still there, even on hot sun-kissed days. As the night falls and the day’s warmth disappears into space, the ground gets ever-colder, chilling the air in contact with it.

Cold air can’t hold as much water as warm air; and so there comes a point when the air touching the ground releases the water it can no longer hold. At this precise moment, dew drops form.

As dawn rises and the sun starts to warm the ground and the air above it, so the water can be re-absorbed again. The dew evaporates – departing as silently as it arrived. And the earth is washed and ready to face a new day.