Water consumption in Slovenia repersents relatively small proportion of the annual gross water outflow from the country, in 2014 the annual index WEI was around 2%, or, comparing to periodic average of water availability, 3%. The Long-term Annual Average Water Exploitation Index shows slight increase, but the trend is not statistically significant .
In recent years, the amount of waste water treated by processes of secondary or tertiary treatment increased, while the amount with primary treatment decreased. The amount of wastewater that was treated with secondary treatment processes, has, since 2002, increased by 150% or 38 million m 3(in 2002) to 60 million m 3(in 2015). Tertiary wastewater treatment was almost nonexistent in Slovenia in 2003, while in 2015 55 % of all treated wastewater, or 73 million m 3 wastewater was treated by tertiary processes.
After above-average 2013 and 2014, 2015 had below-average runoff. Since 1961 only 1983, 2003 and 2011 were drier. The long-term downward trend of river runoff from Slovenian territory, persist.
For the period 2002 to 2005 the improvement of chemical and saprobiological quality of rivers is observed.
Due to changes in legislation this indicator is replaced with the indicator [VD12] Chemical and ecological status of the surface waters by 2006.
Slovenian groundwater bodies most polluted with nitrates are those with intergranular (alluvium) aquifers, particularly in northeastern Slovenia. Groundwater in karst and fractured aquifers is due to geographical conditions, low population density and scarce agricultural land less burdened with nitrates. On water bodies Mura basin and Savinja basin average annual levels of nitrate in the period from 1998 to 2015 show a statistically significant downward trend in nitrate levels. On the other water bodies declining nitrate levels are not statistically significant.
The levels of pesticides in groundwater have been decreasing. In the flat lands of Slovenia (the basins of the Drava and Mura rivers), for which intensive agricultural activities are typical, these levels are still exceeding the quality standards. Individual point sources of pollution can be a result of the unskilled use of plant protection products.
In Europe, the number of lakes with low phosphorus content and greater transparency is increasing, as a result of measures taken to reduce pressures of to lakes and their contributing areas. Compared to the situation in seventies, after the introduction of recovery measures, improvement has been observed in Lake Bled as well, however overburden with phosphorous compounds is still occasionally present, with impact on increased phytoplankton biomass and reduced transparency of the lake. Lake Bohinj is one of the oligotrophic, flow-through alpine lakes where the effects of man in the lake’s water basin, covering a sparsely populated mountain karst area, are relatively mild. The concentration of phosphorous is relatively low and reduces the productivity of phytoplankton. In the artificial reservoirs, especially those in central and north-eastern Slovenia, where agriculture is the main activity, the average content of phosphorus is significantly higher and transparency lower than in natural lakes, with no trend of improvement.
Large and medium supply areas, which supply more than 1,000 people (85 % of the population), generally have adequate quality of drinking water. Out of these, one fifth of population is supplied with drinking water, which does not need preparation. From health prevention point of view, the most uncontrolled are the small supply areas, which supply 50-1,000 people (mainly areas with 50-500 people) because they are polluted with faeces. Similar applies for areas, which are supplied with surface water, which from health risk point of view include karst sources of drinking water. The results of chemical tests show that drinking water is polluted with pesticides and nitrates. Drinking water quality monitoring does not include the population who are supplied by drinking water supply systems for less than 50 persons, so the quality of drinking water for this population is not known (app. 134,000 population in 2015). According to parameters, important for population health, chemical quality for year 2015 is not known for approximately 218,000 Slovenian population. The quality of drinking water did not improve significantly in the period 2004-2015.
Inland bathing water quality in Slovenia is good and comparable with bathing water quality in other European countries.
The values of biochemical oxygen demand, which is usually an indicator of organic pollution, have significantly decreased in Slovenia since 2005. Average levels of nitrate, orthophosphate and ammonium, which are slightly above background levels, do not show significant changes in the period.
In 2014, 21 from 22 sections of surface water met the limit values for water quality for fish life. P>
At five segments (23%), water quality is also above recommended values. In other sections most frequently exceeded values are those for the nitrite, in the salmonid sections also for ammonium.
Around 40,000 water permits and concessions had been granted for special water use in 2016.
Total renewable groundwater quantity in shallow aquifers of Slovenia in hydrological year 2016 was below the long term average of the 30 years period 1981-2010.
Water protection areas cover 347,000 ha or 17% of the territory.