The Pinios Hydrologic Observatory (PHO) covers an area of 53 sq.km and is situated within a complex geological/geomorphological environment with forest and agricultural landscapes dominating. PHO was established in year 2015 with the joint efforts of Agrosphere Institute (IBG-3) of Forschungszentrum Jülich (Germany) and Soil & Water Resources Institute of Hellenic Agricultural Organization “DEMETER” (Greece), aiming primarily at developing deep knowledge of water balance at the river basin scale and to improve understanding of the major hydrodynamic mechanisms, thus to improve hydrological modeling and ultimately sustainable water resources management. Moreover, and since agriculture constitutes the major economic activity in PHO, agro-hydrology constitutes one of its top-priority research topics. PHO is located in the River Pinios basin (RPB), which is one of the most productive basins in Greece having a spatial extent of about 11,000 sq.km. RPB is facing a wide range of problems related to water resources management including groundwater overexploitation and quality deterioration triggered by prolonged droughts and poor management practices in the mid-1980s, which affect and jeopardize the regional socio-economic stability and growth. PHO is envisaging to investigate and address critical scientific questions on how to effectively preserve water and soil resources of the basin and to efficiently manage water availability on the basis of natural recharge occurrence.