Water consumption in Slovenia represents a relatively small proportion of the annual gross water outflow from the country. In 2019, the annual WEI+ index was around 3%, and same 3% compared to the periodic average of water availability. The Long-term Annual Average Water Exploitation Index shows a slight decrease, but the trend is not statistically significant.

In recent years, the amount of wastewater treated by secondary or tertiary treatment processes increased, while primary treatment processes have closed. The amount of wastewater treated through secondary treatment processes increased by 150 % since 2000 or from 30 million m3 (in 2000) to almoust 45 million m3 (in 2019). There were almost no tertiary wastewater treatment processes in Slovenia in 2000, and in 2019, 72% of wastewater or 113 million m3 of wastewater was treated by tertiary process.

The above-average runoff years of 2013 and 2014 were followed by a below-average year in 2015 and a period of average annual runoff from 2016 to 2021. In 2022, runoff levels were again below average, while 2023 saw a return to above-average conditions. Based on the annual river balance, 2023 ranks among the wettest years in the history of hydrological measurements. Between 1961 and 2023, the most water-abundant years were 2013, 2014, and 2023. In contrast, the driest years were 1983, 2003, 2007, 2011, 2015, and 2022.

Groundwater in intergranular aquifers in Slovenia is most affected by nitrate pollution, particularly in northeastern Slovenia. In contrast, groundwater in karst and fissured aquifers is less impacted due to geographical conditions, lower population density, and a smaller proportion of agricultural land.

For the period 2019–2024, poor chemical status was identified in the water bodies of the Savinja, Drava, and Mura basins. The main cause of poor chemical status in all water bodies was nitrate, with atrazine additionally contributing in the Drava basin.

Nutrient over-enrichment remains the key environmental challenge for lakes and reservoirs in Slovenia. For the assessment period 2014–2019, only 4 of the 11 lake water bodies achieved good or high ecological status. Recent annual data indicate no signs of improvement, and in some lakes total phosphorus concentrations are even rising. The main pressures are linked to human activities, especially inappropriate discharge of municipal wastewater, intensive agriculture in the catchments, and fisheries.

In 2023, drinking water monitoring was carried out in supply zones (water supply systems) that supply 50 or more persons (92.3% of the population). Large, medium and some of small supply zones that supply more than 500 (87.7%) inhabitants, generally have adequate drinking water quality. The smallest supply zones that supply 50-500 inhabitants are the least regulated, in comparison to larger due to the fecal contamination, as some with karst water resources.

The quality of inland bathing waters in Slovenia is high, as most are classified as “excellent”, which is better than in the majority of other EU Member States.

The values ​​of the parameters used to monitor the load of rivers with organic substances have decreased significantly since 1996. The observed decrease in organic load corresponds to the increase in the proportion of the population whose wastewater is treated in municipal and joint wastewater treatment plants. The load of rivers with nutrients varies significantly between river basins. The average nitrate values ​​in all river basins of the Danube river basin are higher than in the Soča and Adriatic river basins and above the values of the natural background.

In 2024, we began reporting on the chemical status of groundwater for a longer six-year period, in line with the reporting cycle under the Water Framework Directive. Based on this assessment, the state adopts measures to improve water quality.

In Slovenia, 98.7% of surface water bodies are in good chemical condition. The two water bodies are in poor chemical condition due to the excess of metals. In general, Slovenian surface waters are not loaded with priority substances in the water, but they are loaded with too high concentrations of mercury and brominated diphenylethers in fish. These are ubiquitous pollutants that are excessively present in biota both in Slovenia and in Europe.