For the purpose of water management, the Water Act envisages the defining of water and waterside land data. The register of water and waterside land has not yet been established. Land use data is the first step to the final establishment of the register, as defined by the Water Act. In Slovenia, there are few registers containing data that can be interpreted as part of the water and waterside land in accordance with the act. A comparison of data from the land cadastre, the register of land use of agricultural and forest land and data obtained from tests of water and waterside land was made. We compared the definitions, methods of data capture, data quality and maintenance procedures, and performed visual and spatial comparisons of captured objects. The comparison included a general overview of the ownership of the areas where data from different registers overlap. In conclusion, the essential differences between the registers are presented together with proposals for harmonization of spatially dependent data from different registers. The focus is on proposals to create a single, uniform register of land use. [ABSTRACT FROM AUTHOR]