Data availability

GEMStat hosts a large variety of water quality data from countries worldwide. The regional subdivision follows the classification of UNEP-Regions (i.e. where the United Nations Environment Programme has Regional Offices).

In the following you find background information about the geographic and temporal coverage of GEMStat as well as available station types and parameters.

Geographic data coverage

As of January 2026, GEMStat contains more than 61 million entries (more than doubled over the last year) from over 31,0000 stations in more than 90 participating countries. The largest number of the data by far comes from river stations, followed by data from groundwater and lakes. The largest coverage of stations, as well as sample value coverage, is currently in Europe and Latin America and the Caribbean.

  • Donut chart showing the percentage distribution of values by UNEP region, with Europe having the largest share, followed by Latin America and the Caribbean, Asia and the Pacific, North America, and Africa.
  • Stacked area chart showing the number of values by UNEP region from 1900 to 2025, with a sharp increase after 1980, dominated by Europe and Latin America and the Caribbean.
  • Donut chart showing the percentage distribution of stations in GEMStat by water body type: 61% river stations, 23% groundwater stations, 11% lake stations, 4% reservoir stations, and a small segment for wetland stations.
  • Donut chart showing the percentage distribution of stations in GEMStat by region, with Europe at 51%, Latin America and the Caribbean at 35%, Asia and the Pacific at 10%, and Africa, North America, and West Asia each at 2%.
  • World map showing locations of water monitoring stations in the GEMStat database by type, including river, lake, groundwater, reservoir, and wetland stations, with a legend.

Temporal coverage

GEMS/Water was founded as a global network for water quality monitoring in 1978. Overall, data is available for the time period from 1906 to 2023, covering a total time frame of 117 years. The longest time series are currently available from North America. The most recent samplings (2024 and 2025) are currently available from Belgium, Croatia, Iceland, Ireland, Japan, Latvia, Lithuania, the Netherlands, Portugal, the Republic of Korea, the Russian Federation, Slovenia, and Cyprus.

World map showing countries shaded by year of most recent water data submission, with a legend indicating years from 2023 to before 1991, and some countries marked as no data submitted.

Parameter coverage

Parameters in GEMStat are classified following the CUAHSI Hydrosphere Ontology. In total, more than 600 parameters are available, which are classified into a hierarchical system of groups and subgroups.

GEMStat catalogue (XLSX-File)

Currently, most GEMStat data falls within the category chemical parameters, followed by physical parameters, while biological parameters represent only a minor proportion. The largest proportion is contributed by organic compounds, followed by inorganics, and nutrients.

  • World map showing regional data availability for various parameter groups with pie charts indicating proportions of inorganic, nutrient, organic, oxygen demand, flux, optical, temperature, suspended solids, indicator organism, phytoplankton, and pigment data; some regions marked with diagonal stripes indicating no data stations reported.
  • Stacked area chart showing the number of values by parameter group from 1900 to 2025, with a sharp increase after 1980, dominated by organic and inorganic parameters.
  • Donut chart showing the number of values in GEMStat by parameter group, with the largest segments for Organic (47%), Inorganic (33%), and Nutrient (12%), and smaller segments for Oxygen Demand, Flux, Optical, Temperature, Suspended Solids, Indicator Organism, Phytoplankton, and Pigment.