On a cold morning we may find that grass in our garden is wet but that it has not rained during the night. This water is known as dew. Air nearly always contains some water in the form of vapour or moisture. Usually we can't see this water because it is like a gas, although when the air is humid, the weather may feel 'sticky'.
Humid air contains more moisture than dry air.
When the temperature of air falls however, its ability to hold moisture decreases. If the temperature drops low enough, air can become saturated, even if it was originally much drier at the warmer temperature. At this point excess moisture begins to condense, forming small water droplets on the ground called dew. In Britain, dew is common all the year round, even in the summer. Air in Britain mostly comes from across the Atlantic Ocean and contains a lot of moisture.