The water that reaches the taps of the 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 reclaimed water from the Llobregat have now become the main sources of household supply. This is a Copernican twist that illustrates the extent to which the drought has forced the search for alternative resources to guarantee supplies. Drinking water is less and less dependent on rain from the sky.
Resources from desalination and reuse of regenerated water from the Llobregat are now the bulk of the drinking flows produced in the Barcelona area. These two large taps provide 58% of total water consumption, while conventional traditional sources (rivers and wells) only account for 42%. This is indicated by the data from the company Aigües de Barcelona referring to the 23 municipalities where this water supplier company provides service (with a consumption of 5,850 liters per second).
In April two years ago, 97% of the water resources that reached 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 its filtration membranes. The facilities cannot be stopped.
But this panorama has turned around like the back of a sock. Now the main source of supply is provided by desalination (El Prat de Llobregat station).
Specifically, one third of the total water consumed in these 23 municipalities (33%) is collected from the sea, while one out of every four liters that is drunk in the Barcelona area are reused flows from the wastewater regeneration station of The Prat. For its part, 23% comes from wells, and the fourth most important faucet is now the flow that circulates through the Ter and Llobregat rivers, with a dwindling flow and with reserves that are at a quarter of their maximum capacity.
Due to the drought, the changes have been enormous in the last year, when the Agència Catalana de l'Aigua (ACA) has had to plan to obtain new resources in parallel to the decline in reserves in the reservoirs.
However, the great qualitative leap (and the truly extraordinary one) 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 wastewater from the El Prat treatment plant is not dumped into the sea, but is treated in the regeneration station and is pumped upstream and discharged in Molins de Rei, above the Sant Joan Despí station, where it is makes it drinkable for later distribution.
“To be able to use and treat (make drinkable) this regenerated water, a certain mixture is needed with the water that the river carries; 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 reclaimed water; that is, for every cubic meter of water that goes down the river, we provide one cubic meter of reclaimed water”, they add.
Desalination (from El Prat) is the essential pillar for supply. Its production was running at a minimum in 2021, but this desalinated water factory received a strong boost last year; in April it already contributed almost a quarter of the resources consumed (23%), and its relevant role has continued to increase.
“Desalination production is already at maximum capacity; for the current drought, desalination can no longer work; instead, regeneration can increase its production; and we are going to give more reused water”, say the same sources.
Now, in El Prat, 1,400 liters per second of reclaimed water are produced and work is underway to increase this amount to 1,600 l/s. The result is that regeneration and desalination will be almost on par.
If a broader metropolitan area than that of these 23 municipalities is taken as a reference, the image offered would be very different because outside this region, reclaimed water for drinking use is not consumed.
The only station designed for the indirect reuse of water is that of El Prat. In the rest of the country there are no facilities designed for this purpose. It must also be taken into account that a regeneration plant such as the one in El Prat (which handles water from treated flows) needs to be accompanied or complemented by a water treatment plant such as the one in Sant Joan Despí, so this simultaneous combination is necessary for 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 you take advantage of more? “No, because we don't get more residual water in El Prat; that is the possible production level (1,800 liters per second) because we will be treating 100% of the wastewater that enters us. And if no more residual water enters, we will not be able to produce more regenerative water”, say the technicians.
Under current conditions, all the water that flows through the Llobregat is collected at the Sant Joan Despi station, so once it is made drinkable, the river remains practically dry. For this reason, 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 Despí. A small part is injected into the subsoil to protect the aquifer from saline intrusion and another part goes to farmers, especially on the right bank of the Llobregat.
