Semiarid regions and some oceanic and Mediterranean islands, have the singularity of using the same traditional water exploitation like small dams made from local materials that intercept streams when it rains (run-off harvesting), in the other hand when the land is sloping plots are used. These environments , from around the world, have things in common as torrential rainfall pattern. For this reason they have problems with water erosion and soil conservation. Another point is that in islands and regions with semiarid climate the availability of freshwater is scarce, forests, that can grow in these environments have a crucial role in the regulation of water resources in several ways, they encourage the infiltration, conserve soil and if forests are at some altitude could take advantage from the fog precipitation, this is a typical case in oceanic islands and in some inland areas. In our case studies, there are some hydraulic strategies to increase water and reduce erosion, which occur in some territories such as the Canary Islands in Spain and the semiarid Negev in Israel (and many others in Middle East), where the role of these technologies is conserve soil (traditional techniques mainly), to increase water and finally generate development to the community, forests, agriculture, flora and fauna. In the case of Canary Islands another important factor to understand the water resources regulation in the islands is the fog precipitation. In the Canary Islands this effect occurs from the 600 meters, powered by vegetation adapted to this type of precipitation, also this phenomenon has been observed in the Sahara desert in Africa coast.This paper discusses the peculiarities on each case, highlighting the ability of the traditional techniques to improve the hydrological cycle on lands with scarce of water resources.