The Case Study focus is on the wider Sofia metropolitan area (total area of 3668 km²), as delineated by the borders of the Upper Iskar river catchment.

The Iskar River is the longest river in the Bulgarian part of the Danube River Basin, with significant economic and environmental importance. The permanent population is 1,267,098 inhabitants (2008) but increases above 2,000,000 if non-permanent residents (students and workers) are included.

The average amount of water abstracted in the Upper Iskar basin is around 361 hm³/yr. Only 6% of the water supply concerns groundwater, while the remaining 94% are abstracted from surface sources. Water resources are primarily used for domestic water supply (54.6%), industrial water supply (44.9%) hydroelectricity production, for irrigation (0.5%) and for recreation. A series of water reservoirs have been built upstream, of which two are used for water supply:  Iskar,  the biggest water reservoir in the country (655.3 hm³) and Beli Iskar (1.5 hm³).

Due to the high competition among different water users (domestic, industrial and agricultural) and recurring droughts in the region, efficient water consumption is of crucial importance. Furthermore, urban water delivering, water and wastewater treatment demand considerable amount of energy, whereas the handling of generated sludge during wastewater treatment accounts for almost 50% of the overall operational costs.

According to a recent study, employing life cycle assessment-based methods, the Sofia urban water system addresses the minimum standard for environmental protection and health objectives but is still focused on compliance issues and end-of-pipe solutions. To that end, the economically efficient enhancement of the overall sustainability of the water system, through innovative technologies for water and wastewater management is a highly relevant goal and priority of authorities and local actors.

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