The ongoing drought crisis in Catalonia has sparked growing social and media concern regarding the management of this vital public resource. Eastern Catalonia is currently in a state of emergency, with recent data showing internal basin reservoir levels below 15%. The last water consumption restrictions in Barcelona date back to 1953, highlighting the severity of the current situation.
However, the focus often remains on surface water (lakes, rivers, reservoirs), leaving groundwater overlooked, despite its comparable or even greater volume. Surface water alone cannot meet the water demand of Catalonia’s population, agriculture, and industry. In the absence of sufficient rainfall, alternative resources such as reclaimed or desalinated water are often utilized. But what about groundwater—our aquifers? They are part of the solution, but are they sufficiently studied and valued?
Amid growing alarm, an emerging ecological awareness, and the need for improved management models, the Institute of Environmental Assessment and Water Research (IDAEA-CSIC) highlights the potential of groundwater to meet current water demands and address drought in Catalonia.
Drought does not affect all of Catalonia equally
Catalonia features two distinct geographic zones for water supply and management. Eastern Catalonia’s internal basins are managed by the Catalan Water Agency, while the Catalan Ebro basin, located inland, is overseen by the Ebro River Basin Authority, under the Ministry for Ecological Transition and the Demographic Challenge.
Drought impacts these zones differently. The Ebro River basin maintains reserves at around 70% and is operating normally. In contrast, the internal basins, particularly the Ter-Llobregat system—which serves the densest populations and industries—face a more critical situation.
A map of Catalonia's hydrological basins. | Catalan Water Agency
A drought monitoring tool by the Catalan Water Agency shows the internal basins (colored areas) suffering from reservoir levels below 15%, whereas the Ebro basin (gray) has reserves between 60-70%. | Catalan Water Agency
Most of Barcelona’s water does not come from reservoirs
Water demand in Barcelona presents a significant challenge for achieving sustainable water management. To understand water flow in Barcelona, let’s follow its journey from a home in the Sants-Montjuïc district. Wastewater travels to one of Barcelona’s main wastewater treatment plants (WWTP): either WWTP Besòs or WWTP Baix Llobregat. For instance, wastewater from this home reaches WWTP Baix Llobregat, where it undergoes various treatments to reduce pollutant loads to acceptable levels for its intended use (discharge, agricultural use, etc.).
After treatment, the water is sent to a Water Reclamation Facility (WRF) located next to the WWTP Baix Llobregat. Here, reclaimed water is produced, which is then discharged upstream near Molins de Rei, blending with the Llobregat River to increase its flow.
The reclaimed water flows downstream and is ultimately collected at the Drinking Water Treatment Plant (DWTP) in Sant Joan Despí, where it is purified for human consumption and distributed back to homes.
Distribution of current and planned wastewater, reclaimed water and drinking water in Barcelona managed by Aigües de Barcelona. | AGBAR
Is reclaimed water the solution for Barcelona’s demand?
In 2021, 97% of Barcelona’s water supply came from rivers and aquifers. By 2023, this percentage dropped to 42%, with 58% of the city’s water demand now met by desalinated and reclaimed water.
Since 2009, Barcelona has relied on the Llobregat desalination plant—the largest in Europe for urban supply. This plant converts seawater into potable freshwater, meeting 33% of the city’s water demand in 2023, albeit at a significantly higher energy cost than conventional resources like reservoirs or aquifers.
Reclaimed water—treated wastewater that undergoes additional treatment at WRFs—can be reused for irrigation, street cleaning, industrial uses, and recharging aquifers. While indirect potable reuse is possible (as seen in Barcelona), direct potable reuse is currently restricted under European Union regulations, except under catastrophic conditions.
“Today, more than half of Barcelona’s water comes from desalination and reclaimed water,” stated Josep Lluís Armenter, drought plan coordinator at Aigües de Barcelona, during a conference organized by IDAEA-CSIC and the University of Barcelona.
Armenter advocates for alternative water sources like reclaimed water, which current technology ensures is safe and consumes one-third of the energy of desalination.
Scientific perspective: groundwater is key to sustainable water management
Groundwater often goes unnoticed—hidden from view and thus overlooked by the general public and governing bodies alike. Yet, it is critical for efficient and sustainable water management. To date, most water supply has relied on surface water (reservoirs, rivers) and, more recently, on alternative systems like desalinated and reclaimed water.
Groundwater leakage at the Loue spring, Jura massif, France | Jacques Lhommee
“Groundwater constitutes 90% of the world’s available freshwater, making it a vital resource to address future hydrological challenges like drought. We cannot base all solutions on technological developments and large investments,” states Estanislao Pujades, a hydrogeology expert at IDAEA-CSIC.
Groundwater is a local, abundant, higher-quality, and more cost-effective resource than reclaimed or desalinated water. Aquifers naturally filter suspended solids and can reduce many organic pollutants through physical-chemical processes, offering water of better quality at a lower cost.
In dry years, groundwater available in Catalonia’s internal basins is equivalent to the full capacity of the Sau and Susqueda reservoirs combined, according to Joan Botey i Bassols, a civil engineer and IDAEA-CSIC researcher.
Underground resources available in Catalonia. Left: normal year. Right: dry year. | Prepared by Joan Botey i Bassols based on data from the Catalan Water Agency.
To effectively utilize groundwater resources, it is crucial to understand that the sustainably available resource is not the aquifer’s capacity—how much water it can hold—but rather how much water replenishes it, or the aquifer’s recharge. Overexploitation of an aquifer beyond a certain threshold not only risks severely degrading water quality but also causes permanent compaction of the aquifer, leading to an irreversible loss of the resource.
“The current regulations only protect extraction zones, but if water does not recharge the aquifer, or if the recharge water is contaminated, we are putting this resource at risk and wasting it. Therefore, we should also protect recharge zones,” explains Botey i Bassols.
Several strategies can increase aquifer recharge and, consequently, the available resource. These include making urban soils more permeable to water, designating and adapting areas to facilitate the infiltration of rainwater and river overflows, or artificially recharging aquifers with treated or reclaimed water, either through infiltration or injection methods.
In general, managed aquifer recharge is an effective solution for increasing the availability of freshwater during dry periods. Beyond augmenting water volumes, aquifers naturally enhance the quality of the recharged water through physical and chemical processes, which can reduce the concentration of certain organic contaminants not removed by treatment plants.
“Looking ahead, we need to adopt a more ambitious approach to better address climate change and ensure water availability across all areas and sectors,” emphasizes Pujades.
A watershed-wide approach could be a strong alternative, increasing the basin’s capacity to buffer extreme weather events, maintaining river base flows for longer periods, and maximizing the potential uses and beneficiaries.
“We should enhance and optimize the use of groundwater, as it is a more local and cost-effective resource, while reserving reclaimed and desalinated water as alternative solutions to cover any remaining deficits,” concludes Botey i Bassols.
Alicia Arroyo
Communication and Outreach | IDAEA
