The predominant source of Barcelona's water can change as demand and available resources change. Aigües de Barcelona says taste can vary within the same area from one day to another. Its origin map describes that variability rather than fixing one source for every address.
The wider supply combines several resources and treatment routes. Following them explains why a general source label cannot give the exact blend in a particular glass.
Managing several sources
The Catalan Water Agency describes the metropolitan supply through the Ter and Llobregat rivers, regenerated water, desalination and groundwater. Regenerated water is wastewater cleaned for reuse, as the Catalan government's water glossary explains. In the agency's breakdown, this water joins the Llobregat river route for later drinking-water production; it still goes through drinking-water treatment.
The Ter-Llobregat network council sets operating guidelines according to water availability, the balance between reservoir systems and incidents affecting production. The agency's regional source-management page, updated in January 2026, explains these decisions.
Any percentage needs the date and area it covers. A regional operating example, an annual production total and a supply-zone figure describe different things. A drought report can explain the conditions of its period without describing the blend during your stay.
Treating water at Sant Joan Despí
The utility's Sant Joan Despí process guide starts with river intake, particle settling and sand filtration. Surface water and groundwater meet in a treatment line using ozone and activated carbon. The guide also describes membrane treatment, including reverse osmosis: pressure pushes water through thin barriers that separate it from dissolved salts. The treated streams are then blended and chlorinated.
Groundwater remains a source that needs treatment. Reverse osmosis is one process within a plant handling multiple streams; the guide describes those treated streams coming together. It does not say the whole metropolitan supply comes from one membrane unit.
Desalinating water at El Prat
At El Prat de Llobregat, the ITAM Llobregat plant processes seawater by reverse osmosis. ATL's technical guide describes adding minerals back after the membranes, a step called remineralisation, followed by disinfection with sodium hypochlorite, a chlorine disinfectant, before distribution.
The plant provides another supply option. Its rated capacity is the output it was designed to produce under specified conditions, rather than a measurement of what reached an address today. That depends on the regional operating choices as well as the available sources.
Checking information for your area
Select the relevant area in Aigües de Barcelona's official map for source and water-quality information. If you notice a taste change, check that information or ask the supplier. Flavour alone cannot identify the blend.
For an address-specific question, keep the location and date with the treatment route and operating conditions. This supply explanation does not diagnose building plumbing or certify an individual tap. Our Barcelona water guide has broader visitor context.
