Water reuse and desalination in Spain – challenges and opportunities

This article offers an evaluation of the reuse of reclaimed water and desalination in Spain and aims to provide an overview of the state of the art and Spanish legal framework as far as non-conventional resources are concerned. The ﬁ ght against the scarcity of water resources in this country, especially in the southeast, has made the production of new alternative water resources a clear priority and has turned the nation into a leader in water reuse and seawater desalination. The assessment presented can be used to help build a more general framework, like the European one, and shed light on other comparative legal experiences.


INTRODUCTION
The technologies used in industrial water production, desalination and water reuse represent a key tool for tackling water scarcity, adaptation to climate change and facilitating the implementation of a circular economy. Making use of reclaimed and desalinated water leads to a more sustainable use of the resource and contributes additional new resources. Desalinated and reuse of reclaimed water reduces the exploitation of inland water bodies, surface water resources and groundwater. Thanks to these technologies, new flows are introduced into the hydrological cycle, ecosystems are improved, and pollution is mitigated as less wastewater is discharged into the environment. They also help to ensure sufficient quantities of high-quality water, and play a part in meeting the objectives of Directive Through Agenda 2030 for Sustainable Development, the United Nations is also pressing for worldwide adoption of desalination and reuse technologies, as an essential tool for achieving its Sustainable Development Goals (SDGs). In order to ensure water availability, sustainable resource management and sanitation for all (SDG 6), there must be integrated management of water resources. Furthermore, the percentage of untreated wastewater should be halved by 2030, and a substantial global increase is required in the recycling and safe reuse of treated wastewater. This calls for greater international cooperation in activities and programmes relating to water and sanitation, including desalination, wastewater treatment, and recycling and reuse technologies (SDG 6, Goals 6.3, 6.5 and 6.7, Agenda 2030 for Sustainable Development).
Countries facing water scarcity have long been aware of the potential of these technologies for combatting water shortages. In Spain, which suffers from a chronic structural water deficit, water reuse and desalination have been a priority for some time now. The government's White Paper on Water published in 2000 acknowledged that the use of non-conventional water resources equated to only 1% of the available conventional resources; it thus proposed specific, ground-breaking legislation to promote the two abovementioned technologies, while ensuring the required level of safety in all aspects (legal, public health, technological, etc.). In particular, the reuse regulations are fairly stringent: Royal Decree 1620/2007 (RDR) sets out the legal standards for the reuse of reclaimed water, establishing very rigorous criteria in Annex I.A based on maximum permissible values (MPV), and stipulating numerous water quality analyses. This legal framework will be discussed in more detail below, with a particular focus on its application in the Region of Murcia. It is, however, something of a paradox that, in Spain, there are quality regulations that govern the use of reclaimed water for irrigation, but not the use of water directly sourced from natural watercourses (Hernández ).
Spain has a highly variable rainfall regime, averaging over 2000 mm/y in some areas (Galicia, the Cantabrian Mountains, the Basque-Navarran Pyrenees, the Central Mountain System and the Sierra de Ubrique) but less than 200 mm/y in the southeast (Almeria and Murcia), one of the lowest rainfall levels in Europe. This complicated water balance is becoming particularly acute in some areas of the country; the Mediterranean coast, which already suffers from water scarcity, is the region worst hit by droughts. Practically all surface water resources in Spain are already stored in reservoirs, and so no new reservoirs are scheduled for construction in the near future. Furthermore, in many cases, groundwater resources are overexploited.
In view of the circumstances described above, no significant future increases are expected in available water from conventional sources, and so in the most vulnerable areas a key role will be played by alternative sources such as reclaimed water and desalination of brackish water and seawater.

WATER REUSE IN SPAIN
Reuse as a tool for sustainable water policy The use of reclaimed water is a tool in the comprehensive, sustainable and cost-effective management of water. It represents a promising option in countries facing water scarcity and drought, such as Spain (Martin ). In this country, water reuse helps to solve issues concerning insufficient allocation of resources to certain uses, halts the degradation of public water resources and the overexploitation of aquifers, and reduces environmental pollution ( Figure 1 and Table 1).
Water reuse is an industrial process that enables an additional use of previously used water before it returns to the rivers or the sea, and after it has undergone a wastewater recovery and treatment process that ensures the legally required quality. The ultimate goal of this process is to secure new resourcesreclaimed waterthat can be directly offered to other users or exchanged for better quality water. The use of reclaimed water frees up other sources of water, which can then be employed for more strictly controlled uses such as human supply, thus contributing to a more rational use of water (Navarro ).
It is worth clarifying the difference between treated water and reclaimed water, as they are subject to different regulations. RDR defines them as follows: Treated water is wastewater that has been treated at the urban wastewater treatment plant (WWTP) to ensure its quality meets wastewater discharge authorization requirements (Article 2 b, RDR). Such water can be returned to any bodies of water as it will not alter their ecological status, and is in fact diluted by its discharge into the receiving water bodies.
Reclaimed water is wastewater that has been submitted to a more rigorous treatment process in a water reclamation facility (WRF) and can thus be directly employed for more restricted uses (irrigation, industrial uses, environmental uses, etc.), without being diluted by other water flows (Article 2 c, RDR). The intended uses for reclaimed water determine the quality criteria that will be applied in the WRF and that are set as mandatory minimum requirements.
In Spain, the use of reclaimed water helps ensure that there is enough water to meet existing requirements, rather than enabling an increased demand. The aim is to guarantee a regular, reliable water supply, as well as to halt the degradation of water bodies. Since reclaimed water represents a net addition to the water in a river basin, it allows better use of the available flows in each season. Reclaimed water can be used for crop irrigation; can be discharged into perennial streams or into dry channels that filter into an aquifer; or can be returned to the sea.

Legal framework
There are no Europe-wide regulations governing specific uses of reclaimed water although there are quite a number of Directives regulating particular aspects of the protection of water resources, which affect reuse and result in varying legal standards (Molina & Melgarejo ). In Spain, however, there is an established legal framework, RDR, which sets out the legal standards for the reuse of reclaimed water.
What can reclaimed water be used for?
Spanish law allows the reuse of reclaimed water for certain urban, agricultural, industrial, recreational and environmental uses. In all cases, the public health authorities must first issue a binding report in which they confirm that the proposed uses are appropriate, taking into account the technical proposal, the self-monitoring programme and the risk management programme presented by the applicant for the concession or authorization.
To that end, the Region of Murcia's public health authority requires that the technical proposal should detail, among other things: the wastewater treatment (at least secondary treatment) with a record of the analyses carried out on water at the outflow of the WWTP; and the reclamation treatment, with a diagram of the reclamation process. The tertiary treatment required depends on the intended use; filtration and disinfection is recommended as a minimum. A record of the analyses carried out on water at the outflow of the WRF is also required.   and toxic substances including priority substances (for certain uses and in accordance with related legislation) ( Table 2).
The use of reclaimed water for human consumption is prohibited, except in situations where a state of emergency has been declared, in which case the public health authority will specify the necessary quality levels for that water. Similarly, reclaimed water is prohibited for uses relating to the food industry, including the manufacture, treatment, conservation or sale of products and substances intended for human consumption; nor is it allowed for cleaning surfaces, objects or materials that may come into contact with food,

How to get a water use permit
The RDR establishes different administrative titles depending on who is applying to use reclaimed water. If the applicant is a third party, that is, someone who is neither a primary-use concession holder nor a discharge permit holder, he or she must obtain a reuse concession from the Administration (the corresponding regional water authority). To do so, these applicants must follow the procedure set out under Spanish water legislation, which stipulates that a reuse plan must be submitted, as part of a competitive call for proposals from potentially interested parties (RDR Article 10).
On the other hand, if the person applying to use reclaimed water is already a primary-use concession holder, he or she must obtain a reuse concession, but in this case does not have to compete with other proposed uses. These applicants will thus have priority over third-party applicants.
Nevertheless, although the simplest approach would be to amend the existing concession to cover the requested reuse,  Irrigation of crops with a water application system that allows the reclaimed water to come into direct contact with the edible parts of crops intended for human consumption and to be eaten raw 2.2. a) Irrigation of crops intended for human consumption with a water application system that does not prevent the reclaimed water from coming into direct contact with the edible parts; however, the crops will undergo subsequent industrial treatment rather than being eaten raw b) Irrigation of pastures for feeding milk-or meat-producing livestock c) Aquaculture 2.3. a) Localized irrigation of tree crops where reclaimed water is prevented from coming into contact with the fruits intended for human consumption b) Irrigation of ornamental flowers, nurseries and greenhouses, without direct contact between the reclaimed water and the produce c) Irrigation of industrial (non-food) crops, nurseries, silage, cereals and oilseeds Articles 3.3 and 3.4) and also exempts them from having to submit a competing proposal. This is because the legislation aims to promote water reuse; discharge permit holders already have the necessary infrastructure for wastewater treatment and will be able to take on the activity at a lower cost. However, it is clear that prioritizing such users confers an additional benefit on the main discharge permit holders, town councils and public sanitation companies, which already charge for the treatment services they provide (Bravo ).
It should be noted that one of the main problems with assigning reclaimed water is the fact that owners of treatment facilities (for example, town councils) do not typically have a discharge permit; moreover, those who do hold a discharge permit are not normally the owners of the land where the reclaimed water will eventually be used (a requirement stipulated in Articles 8 and 9). This means that those applying to use reclaimed water generally have to go through the most onerous procedure to gain reuse rights; namely, the pro- it is on the leeward side relative to the westerly winds, close to a subtropical subsidence region and in close proximity to Africa. In addition, it is set back from the western Mediterranean basin, and the fairly mountainous terrain creates a foehn effect on the westerly flows and provides shelter from Atlantic storms (Gil ). Furthermore, this part of the peninsula is vulnerable to desertification as a consequence of its physical framework which incorporates climatological, edaphological, vegetation and anthropic variables. Increasingly common water scarcity situations lead to direct impacts triggering a chain of desertification effects, which in the long term also affects soil quality (López ) (Figure 4).

Water reuse in the Region of Murcia
The Region of Murcia forms part of the most water-stressed river basin in Spain (Navarro & Martínez ). The imbalance of water resources in this basin and recurrent drought has driven continuous improvement in water management.
In particular, given the historical and socio-economic importance of agriculture in this region, the reuse of water in agriculture has been a key priority: of the 154,680 hectares of irrigable land, 100,337 (64.86%) can make use of water from WWTPs (ESAMUR ) (Figures 5 and 6).
As a result, the region has made major efforts with respect to the reuse of reclaimed water. Its determined push towards the reuse of reclaimed water began with

The general sanitation and wastewater treatment plan
The PGSD laid out three objectives.   (Figures 7 and 8).
The PGSD has also had notable environmental effects: (1) it has combined wastewater reclamation with the conser-

SEAWATER DESALINATION IN SPAIN
In Spain, the desalination of seawater is no longer a marginal hydrological policy option, but rather has become one of the preferred alternatives. Until fairly recently, this method was used almost exclusively in the Canary Islands, which, especially in the eastern islands, face similar water scarcity issues as the south of the Iberian Peninsula. In fact, the drought that hit a large part of the Iberian Peninsula in the early 1990s sparked interest in the options that yield new water resources. This interest has been growing in light of the inescapable fact that water scarcity is not a temporary, passing problem, but rather a global priority issue (Embid ).
The firm commitment to this system for obtaining non-  At the time, desalination was considered an extremely promising option, if production costs could be brought down.
The high cost of desalination: a pending issue It soon became clear that desalination would have to overcome certain difficulties in order to become a viable alternative. Physical limitations and high prices suggested that only a few specific uses of desalinated water would be cost-effective: urban water supply or the most economically competitive agricultural production (Embid ). These concerns have proved to be well founded.
Today, the cost of desalination in Spain remains a major obstacle to achieving its full potential. Moreover, this cost has increased in the last few years due to the liberalization of the Spanish energy sector. Although the development of state-of-the-art membranes can help cut energy consumption in desalination systems, it seems that improving the process is not enough, in and of itself.
Other options should also be considered, such as cogenera- Desalinated water, public water, private water In Spain, desalinated water has been considered either public water or private water, depending on the legislative programme of the government of the day (González-Antón

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T. Navarro | Water reuse and desalination in Spainchallenges and opportunities Journal of Water Reuse and Desalination | 08.2 | 2018 ). Desalination was first regulated by Royal Decree 1327/1995 on seawater desalination facilities. At that time, desalinated water was deemed public water, as it was considered part of the public water resources; that is, once it had been produced, desalinated water was introduced into the water cycle along with inland water and renewable groundwater resources. However, during the sixth parliamentary term (1996)(1997)(1998)(1999)(2000), Spanish legislation allows both public desalination operations (TRLA Article 13.2) and private initiatives (TRLA Article 13.5). The desalinated water produced by private parties can be used to supply residential developments, holiday resorts that lack sufficient resources, and even for irrigation.
The public administration can develop desalination operations, building infrastructure through public works that can be declared to be in the general interest of the State.
These public works can be run directly by the Ministry, by regional water authorities or by commercial companies set up for this purpose (e.g. Acuamed). Irrigation communities can also be direct beneficiaries of the works and facilities in their area; they can be granted the concession for desalinated water directly, without having to compete with other potential users for the rights.

Desalination in the Segura River Basin
The SRBD suffers from a structural deficit. The available resources do not enable the achievement of good water status (one of the basic objectives of the WFD), nor do they meet the demands of its users. As a result, water has to be transferred from other basins, which makes the SRBD unique among Spanish river basin districts.
A central tenet of river basin planning in the Segura River Basin has always been that, in order to accomplish environmental goals relating to groundwater bodies, the over-  Table 4.

CONCLUSIONS
The current shortage and uneven distribution of water resources is a global problem. Even in areas where rainfall or freshwater resources are abundant, shortages can occur, which are exacerbated by population growth and the rising water demand in agriculture, industry and households.
Moreover, drought and scarcity have been endemic problems in certain countries in southern Europe, such as Spain, which has long sought to tackle these extreme hydrological situations and has a mature and well-developed legal framework for doing so.
The global nature of water scarcity challenges cannot be addressed in isolation from the similarly pressing problem of climate change, as the two are directly connected. Several studies have shown that the incidence of droughts in Europe has increased by 20% since 1976, and although the frequency of torrential rainfall will increase, average annual rainfall is set to decrease throughout Spain, with a   Downloaded from https://iwaponline.com/jwrd/article-pdf/8/2/153/240726/jwrd0080153.pdf" /><meta name="description" content="Abstract. This article offers an evaluation of the reuse of reclaimed water and desalination in Spain and aims to provide an overview of the state of the art a particular impact on the southern third of the Iberian Peninsula.
Faced with this scenario of increasing global scarcity and drought, industrial water production techniques such as desalination and reuse have started to play a more prominent role. This paper has shown the legal framework and current status of these techniques in Spain, a country which has come to be recognized as a key point of reference in this respect. This can help in the construction of a more general framework, like the European one, and shed light on other comparative legal experiences.
The fight against the scarcity of water resources in Spain has made the production of new alternative water resources a clear priority, turning the country into a leader in reclaimed water use and seawater desalination, especially in the southeast. The call to regulate this activity and make it sufficiently robust in all aspects (legal, public health, technological, etc.) led to the approval of pioneering state regulation in Spain. As a general rule, reusing reclaimed water requires a permit. However, if it is requested by the holder of a discharge permit, only a supplementary administrative authorization is required, which goes against the general regime for using public water resources in Spain.
On the other hand, Article 13 of TRLA sets out the Spanish legal regime governing desalination. It establishes that desalination is subject to the regime exclusively for public water resources, meaning that a concession is required, notwithstanding applicable authorizations and approvals in accordance with specific legislation.
In summary, it can be said that reuse and desalination have gained importance over recent years in countries that suffer from drought and water scarcity. In Spain, the most well-developed and widely implemented technique is the reuse of water, mainly for agricultural use, although urban and industrial uses have also reached significant levels. With regard to desalination, while there has been clear political support for it, its high production costs continue to be an issue, and users have demanded reduced rates for desalinated water.
In view of the finite nature of water and global increases in demand, an ongoing commitment to industrial water production on a worldwide level is crucial. Governments must continue to drive research, development and innovation programmes (R&D&I), thus boosting related technological progress, and resulting in the implementation of programmes that will enable them to 'do more with less' in their territories, thereby promoting a rational and sustainable use of their water resources.