Diversity of Galician water beetles (Coleoptera: Gyrinidae, Haliplidae, Noteridae, Hygrobiidae, Dytiscidae and Hydrophiliade) was analyzed using a database created by collecting species records from several data sources. Most data came from a long-term sampling program carried out by one of the authors across the whole region but further local studies provided additional data. To assess the inventory completeness as well as to estimate the species richness, both an asymptotic model and some non-parametric estimators were used. Database records were utilized as a sampling-effort surrogate. Total richness estimations predicted by these different methods range between 117 and 131 species. Therefore, it seems that between 86 and 97% of the beetle fauna belonging to the studied families was recorded, so that the inventory has reached an acceptable level of completeness (113 species). A list of the Galician species of Gyrinidae, Haliplidae, Noteridae, Hygrobiidae, Dytiscidae and Hydrophilidae is given.