The paper is aimed to determine the quantity of water which under diverse atmospheric conditions may evaporate from a roof with a construction and covering used to cover storage facilities in the region of Krakow. In order to determine the quantity of evaporation research was conducted in the period from April to October in the form of a tailor-made experiment – at the experimental station equipped in a roof moistened by means of spraying and the automatic meteorological station. Values and variation of water evaporation during night and daytime of the whole research period and particular months have been presented. The average daily and hourly evaporation of water from the roof have been calculated. During the research the evaporation of water from the roof was variable. In every period of measurement the sum of evaporation during the day was several times higher than the evaporation at night. It shows that it is better for water to evaporate on the roofs during the day. The presented data can be used to estimate the area of the surface necessary to evaporate a particular amount of water from the roof provided identical structure of the roof and sprinkler system is used.