The management of rainwater runoff represents an important aspect of water and wastewater management. Different methods exist in order to prevent flooding and erosion as well as to restore the natural hydrological water cycle. In contrast to off-site methods where the rainwater is collected, conveyed and discharged into waterways, rainwater infiltration and the use of rainwater by means of rainwater harvesting allow to address these issues and thus improve the water supply. This lesson covers some of the basic principles which are essential for the design of rainwater facilities. Then, rainwater infiltration techniques and their design are illustrated. The third part of this lesson introduces the concept and techniques of rainwater harvesting, which aims at storing stormwater runoff for the use in agriculture or domestic purposes. This lesson is rounded off with with the presentation of several Tunisian water harvesting techniques as they are applied in semi-arid and arid regions.