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 years 2013 and 2014 were followed by below-average year 2015 and average period 2016 – 2021 of annual runoff. In the year 2022 annual runoff was below-average. In the period 2016 – 2021, the driest years were 2003, 2011, 1983, 2022, 2007 and 2015. The downward trend of river runoff from the territory of Slovenian currently persists.

Slovenian groundwater bodies most polluted with nitrates are those with intergranular (alluvium) aquifers, particularly in north-eastern Slovenia. Groundwater in karst and fractured aquifers is less burdened with nitrates due to geographical conditions, low population density and less agricultural land. In the period 1998–2020, the average annual levels of nitrates in water bodies in the Sava valley, Ljubljansko barje, Savinja, Drava and Mura basins show a statistically significant downward trend. In other water bodies, nitrate levels are not statistically significant.

In Slovenia, nutrient overloading is still the basic problem concerning lakes and reservoirs, and from 2006 to 2019, no improvement is observed. In the assessment period 2016–2019, only 4 out of 11 lake water bodies were determined to be in good or very good trophic status. Overloading of lakes with phosphorus is usually a result of inadequate wastewater drainage and intensive agriculture in the watershed area.

In 2022, drinking water monitoring was carried out for 93.8% of Slovenia's population across 863 supply zones that serve 50 or more people. Large and medium-sized zones, serving more than 500 inhabitants, generally maintain a good water quality. The greatest issues are found in smaller zones (50-500 inhabitants) with a higher percentage of fecally contaminated samples. Chemical contamination was detected in two zones, mainly due to exceeded levels of lead and the pesticide desethyl-atrazine.

Inland bathing water quality in Slovenia is good and comparable with bathing water quality in other European countries.

Values ​​of parameters used for monitoring the organic loading of rivers have greatly reduced since 1996, however ammonium levels remain much higher than natural background. The observed reduction in organic loading corresponds to an increase in the share of population whose wastewater is treated at wastewater treatment plants. The nutrient loading varies considerably among rivers of the Adriatic and the Danube river basins.

Groundwater is most polluted in aquifers with intergranular porosity in the northeastern part of Slovenia.

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.