Romania and Bulgaria started to develop in partnership a system of monitoring, warning and dissemination of data on the quality of environment in the border-area counties. The project it is achieved under the strategic project WATER - integrated water management and is financed under the Romania - Bulgaria Cross-border Cooperation Programme 2007-2013. The project goal it is to establish a common management and control system of the quality of the Danube waters under extreme conditions, caused by natural and technological disasters. The project area includes about 500 km on Romanian and Bulgarian common Danube border area. In order to implement the designed activities in the project area, one of the major infrastructure needed it is the geodetic network and based on that a geo-database including digital maps, specific data and metadata, GIS applications, et al. Along the history, from geodetic point of view, for different activities on the Danube (navigation, water level and quality monitoring, floods management) different kinds of Coordinate and Reference Systems (CRS) were used by Danube countries. For the Romanian-Bulgarian sector, an important issue of this project it is the establishment of a common CRS including horizontal and vertical position. Technical University of Civil Engineering Bucharest (TUCEB - Romania) and Executive Agency for Exploration and Maintenance of the Danube River (EAEMDR - Bulgaria) are the responsible partners for Activity 6 of the WATER project. The main goal of the Activity 6 it is to adopt and to implement a common CRS according to the European INSPIRE Directive. This paper presents geodetic research and applications performed on Activity 6 of the WATER project in order to establish coordinates conversion and transformation standards. The theoretical and practical implementation of horizontal CRS, named ETRS89 (European Terrestrial Reference System) and vertical CRS, named EVRS (European Vertical Reference System) are presented. Research on possible connections between these CRS and previous CRS (as Black Sea 1975 and Baltic Sea) are investigated. The final results of this activity can contribute to the modern realization of the most recent connection between the national geodetic networks of Romania and Bulgaria. [ABSTRACT FROM AUTHOR]