The water that reaches the taps of houses in the Barcelona area no longer comes mainly from rivers (Llobregat, Ter) and wells, as was traditional. The flows from modern desalination technologies and the reuse of regenerated water from the Llobregat have now become the main sources of domestic supply. It’s a Copernican turn that illustrates the extent to which the drought has forced people to look for alternative resources to guarantee supplies. Drinking water depends less and less on rain from the sky.
The resources from the desalination and reuse of regenerated Llobregat water are now the bulk of the potable flows produced in the Barcelona area. These two large taps contribute 58% of total water consumption, while conventional traditional sources (rivers and wells) only represent 42%. This is indicated by the data of the Aigües de Barcelona company referring to the 23 municipalities where this water supplier provides service (with a consumption of 5,850 liters per second).
In April two years ago, 97% of the water resources reaching homes came from conventional sources. Specifically, its origin was rivers (two-thirds of consumption: 63%) and groundwater wells (one-third: 34%), while desalination contributed the remaining 3% and reuse was not underway. It was a symbolic sum. This 3% desalination is due to the fact that this technology must work with a minimum regime for maintenance reasons, necessary for the proper functioning of the filtration membranes. Installations cannot be stopped.
But this panorama has turned upside down like a sock. Now the main source of supply comes from desalination (Prat de Llobregat station).
Specifically, a third of the total water consumed in these 23 municipalities (33%) is captured in the sea, while one in four liters that are drunk in the Barcelona area are reused flows from the regeneration station of El Prat waste water. For its part, 23% come from wells, and the fourth most important faucet is now the flow that circulates through the Ter and the Llobregat, with a decreasing flow and with reserves that are a quarter of their maximum capacity.
Due to the drought, the changes have been enormous in the last year, when the Catalan Water Agency (ACA) had to plan to obtain new resources in parallel with the decrease in reserves in the reservoirs.
However, the great qualitative leap (and the truly extraordinary) is due to the contributions of reused water (25% of consumption), regenerated at the El Prat station, where the flows are subjected to filtration processes. Thus, the waste water from the El Prat treatment plant is not thrown into the sea, but is treated at the regeneration station and is pumped upstream and discharged to Molins de Rei, above the Sant Joan Despà station. where it is made potable for later distribution.
“To be able to use and treat [make potable] this regenerated water, a certain mixture with the water carried by the river is needed; more or less in the same proportion”, say sources from Aigües de Barcelona. “We can say that the necessary flow is being released to be able to mix with the water in equal proportions to the regenerated water; that is to say, for every cubic meter of water that goes down the river, we contribute a cubic meter of regenerated water”, they add.
Desalination (from the Prat) is the essential pillar for supply. Its production was operating at a minimum in 2021, but this desalinated water factory received a strong boost last year; in April it already provided almost a quarter of the resources consumed (23%), and it has continued to increase its relevant role. “Desalination production is already at maximum capacity; for the current drought, desalination can no longer work; on the other hand, regeneration can increase production, and we will give more reused water”, say the same sources.
Now, El Prat produces 1,400 liters per second of regenerated water and work is underway to raise this amount to 1,600 l/s. The result is that regeneration and desalination will be almost equal.
If a broader metropolitan area than these 23 municipalities is taken as a reference, the picture offered would be very different, because outside this region, regenerated water is not consumed for potable use.
The only station designed for the indirect reuse of water is the Prat. In the rest of the country there are no facilities designed for this purpose. It should also be borne in mind that a regenerating station like the one in Prat (which moves water from purified sewage) needs to be accompanied or complemented by a water treatment plant like the one in Sant Joan DespÃ. Therefore, this simultaneous combination is necessary so that its absence is not a limiting factor.
In the future it is estimated that up to 1,800 liters per second could be regenerated. Can’t take advantage of more? “No, because we get more waste water in the Prat; this is the possible level of production [1,800 liters per second] because we will be treating 100% of the waste water that enters us. And if no more waste water comes in, we won’t be able to produce more regenerating water”, say the technicians.
Under current conditions, all the water that flows through the Llobregat is captured at the Sant Joan Despi station, which is why, once it is potable, the river remains practically dry. That is why the maintenance of the ecological flow in the lower section of the river is guaranteed with other contributions
However, not all the water regenerated in El Prat goes to Sant Joan DespÃ. A small part is injected underground to protect the aquifer and prevent saline intrusion, and another part is allocated to farmers, especially on the right bank of the Llobregat.