The Llobregat River flows approximately 170 km from the Pyrenees
Mountains to the Mediterranean Sea, discharging near the
city of Barcelona. The 4950-km2 river basin accommodates 5 million people, including more than half of the Catalan population.
Treated urban sewage, industrial effluents and agricultural runoff
affect the quality of raw river water, which is the main source of
treated drinking water for Barcelona and its metropolitan area. In
fact, the urban water supply constitutes 65% of the total Llobregat
water demand (ACA, 2012). The annual average river discharge
volume is 690 cubic hectometers/second (hm3/s), of which over
40% consists of effluents from the approximately 50 wastewater
treatment plants (WWTP) located within the Llobregat river
catchment area (annual mean discharges: 300 hm3/s) (ACA, 2012).