Incidental potable water reuse in a Catalonian basin: living downstream

A preliminary assessment of incidental potable water reuse (IPR) in the Llobregat River basin has been conducted by estimating the dilution factor of treated effluent discharges upstream of six river flow measurement sections. IPR in the Llobregat River basin is an everyday occurrence, because of the systematic discharge of treated effluents upstream of river sections used as drinking water sources. Average river flows at the Sant Joan Despi measurement section increased from 400,000 m(3)/d (2007) to 864,000 m(3)/d (2008) and to 931,000 m(3)/d (2013), while treated effluent discharges upstream of that section ranged from 109,000 m(3)/d to 114,000 m(3)/d in those years. The highest degree of IPR occurs downstream of the Abrera and Sant Joan Despi flow measurement sections, from where about half of the drinking water supplied to the Barcelona Metropolitan Area is abstracted. Based on average annual flows, the likelihood that drinking water produced from that river stretch contained treated effluent varied from 25% (2007) to 13% (2008) and to 12% (2013). Water agencies and drinking water production utilities have strived for decades to ensure that drinking water production satisfies applicable quality requirements and provides the required public health protection.