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Given the current drought situation, the professor of Underground Hydrology at the UPC, Xavier Sánchez Vila, is committed to combining solutions, such as obtaining water from reservoirs and aquifers with desalination and regeneration. In this new scenario posed by climate change, Sánchez Vila defends the need to create a mechanism that allows water to be regenerated as many times as necessary, in an infinite circular economy cycle.

Xavier Sánchez Vila is a professor at the Higher Technical School of Civil Engineering, Canals and Ports of Barcelona, ​​a researcher in the Underground Hydrology group and director of the Department of Civil and Environmental Engineering at the Polytechnic University of Catalonia – Barcelona Tech. Some areas in which that investigates are the recharge of aquifers, emerging compounds, water resources or reactive transport in heterogeneous media, all to seek solutions to problems derived from the lack of water posed by the climate crisis.

What options do we currently have to stop the drought?

There are many solutions, but each one, independently, is useless, the only solution is the combination of all of them. On the one hand, we have conventional resources, such as swamps and groundwater or aquifers. And then, we have non-conventional ones, such as desalination plants, water regeneration and other possibilities, such as carrying water in ships, network interconnection or transfers. When there is sufficient availability of water, the cheapest solution is always resorted to, which are usually reservoirs, from where the water is extracted to pass it to the rivers, from here to the purification plants and finally to the services. Depending on the point of drought in which we find ourselves, one solution becomes more relevant than the others.

In this sense, can resources such as desalination and regeneration be combined?

Yes, their performance is independent, but they complement each other. Desalination consists of obtaining water from the sea and extracting the salt by reverse osmosis. It is a method with very high energy consumption, the most expensive solution possible. Very good quality water is obtained, but it is returned to doubly salty water. With regeneration, water from wastewater treatment plants is captured and purified. Once purified, it is still not drinkable water and requires another, more complex treatment to put into service. It cannot yet be added to the network directly, but it could be used for irrigation, for example.

What is the role of aquifers in this framework?

Aquifers have an advantage over swamps, which is not being on the surface. In this sense, these groundwater do not evaporate and pollution problems are minimal. It is a very good source. In fact, about fifteen towns in Catalonia are supplied with groundwater, through wells, and do not have any restriction problems. Wells offer a lot of water and of very good quality, although not all of Catalonia can be supplied with wells, which is why it is necessary to combine solutions. Aquifers are filled naturally, but they can also be filled artificially, through what is called managed aquifer recharge. These are one of the elements we work with in the Underground Hydrology research group at the UPC.

How can aquifers be cared for and maintained to make them useful in times of drought?

It is necessary to explore them little by little to try to prevent them from running out of water. They have to be well taken care of when there is a lot of water, what I call “invigorating an aquifer”. The amount of water that infiltrates the aquifer can be increased, water that can come from the regeneration plants. Once we have water again Instead of throwing it into the river, it could be taken to the aquifer to be used when the next drought hits.

In this context, one of the solutions proposed is the transfer of water with boats. Is this measure useful?

I think it is not a good solution, because the quantity is very small. If one ship came a day it would be carrying approximately 2% of the consumption of the Barcelona Metropolitan Area. Furthermore, it is an even more expensive option than desalination, the cost would be unaffordable. There has been talk of using this solution only to supply emergency needs, such as hospitals, but then the water would have to be transferred from ships with tankers or some other system, we would have queues of thousands of trucks waiting to receive the water. and transport it to each different place. Before, other measures would be imposed, such as restrictions, lowering the tap pressure… Unless the situation reaches a very worrying limit, then it may be an emergency option.

If we put ourselves in the worst scenario, when is a critical point supposed to be reached to ask for transfers and external help?

It depends on how it is prioritized and the moment in time where it is preferred to incorporate the supply cuts. Then it would be necessary to activate the transfers, reduce the pressure or make temporary cuts. This last solution is not positive either, because it reduces the useful life of the pipes, since they must always be soaked and it is not advisable for them to remain empty, because, if the water does not pass, they are damaged. This situation would require constant network renewals, and this is very expensive. The priority is more political than technical.

Within this setback that the water cycle is suffering, what margin can be reserved for optimism?

It is a cycle, indeed, but we have manipulated nature so much that it seems that this cycle has changed. Historically, we have always had droughts. In the Mediterranean, the normal situation is that they occur with a margin of between 10 and 14 years. We can say, therefore, that the current drought has arrived when it should, because the last one occurred in 2008. However, what was not foreseen is taking a very long time. When will the next one come and how extensive will it be? It can be conjectured that this cycle will be reduced, perhaps to 8 or 10 years, and that they will extend longer over time. Can we say that as a society we have reacted late to this problem?

As a society we are late due to a problem of lack of knowledge. It is thought that all the water we have comes from rivers and that the only solution to the lack of rain is desalination, we do not think about groundwater, or aquifers. The Catalan Water Agency is not aware of this, because it has very good professionals in general and hydrologists in particular, but they need financial support from the Government. No matter how well the actions are planned, perhaps only a small part is insufficiently executed. It is a problem of lack of investment and prevention, of not thinking about the drought until it is upon us. Now we have to think about solutions for the next drought, with this one we will do what we can.

How to prepare for the next drought?

It is necessary to invest in regeneration, we need many more plants for this activity. Now we have a certain amount of wastewater, it is treated in the treatment plant as always, and instead of dumping the surplus into the sea, we could expand this water to many uses, even if it is not potable. In this moment of emergency, what is called a pro-potabilization treatment is carried out: the wastewater is evoked in the river, recovered and put back into the system. But if it rains and the swamps are filled, this water will not have to be thrown into the river because it will already be full enough. The proposal would be to take this extra water and store it in the aquifers. Thus, in the future, when the swamps recede again, the aquifers will be full and it can be poured into the river and regenerated again. As far as desalination plants are concerned, an increase in this resource would increase the bill too much. In the event of a repeat energy crisis like the current one, the price of water would be exorbitant if we relied only on this resource.