The air in our homes contains water vapour in varying quantities with warm air holding more water than cold air. Air is saturated when it cannot contain any more water vapour and its relative humidity (RH) is 100%. If the temperature then falls until saturation point occurs, the air will reach a temperature at which it cannot hold any more water. This temperature is known as the dew point. Any further fall in temperature results in vapour being forced to condense as liquid water. This water usually appears as droplets or film on non-absorbent surfaces such as windows or tiles and is referred to as surface condensation.