This paper aims at systemizing knowledge related to geodiversity assessment for water resources and its evaluation. The novel aspect connected to geodiversity of this paper is the analysis of the components of hydrological system, both at the superficial and underground level, in the territory of the Sesia Val Grande United Nations educational, scientific, and cultural organization (UNESCO) Global Geopark (Northwest Italy). More specifically, the research establishes a conceptual model and a specific procedure for the evaluation of geodiversity connected to water resources on a regional scale, by means of a qualitative-quantitative geographic information system (GIS) process, renamed here as hydro-geodiversity assessment. For these purposes, a targeted ecosystem approach is applied to consider the assets of the Geopark territory that has been derived from the interaction between water and other components of geodiversity, i.e., the hydro-geosystemic services. The element selection and processing operations led to the identification of areas characterized by greater values of hydrological geodiversity, in which the link between surface and underground hydrodynamics became closer and intense. The single geodiversity factor maps that were obtained from partial data aggregations were added together in map algebra operations, then subjected to weighing to formulate the hydro-geodiversity map of the Sesia Val Grande UNESCO Global Geopark. The results of the present study strengthen the strategic management of geological, geomorphological, and hydrological heritages of the study area by identifying different landscapes and local peculiarities determined by mutual influences between geology and hydrological dynamics.