RICHWATER nutrient management tool and WEFE implementation strategies in South Spain

The Axarquía region (South Spain) faces a convergence of agro-environmental, climatic, hydrological, and socio-economic pressures that have deepened its chronic structural water scarcity. Prolonged droughts and increasingly erratic rainfall, coupled with declining reservoir storage and aquifer overexploitation, are undermining the reliability of traditional water sources. At the same time, the rapid expansion of water-intensive subtropical crops, together with sustained population growth and intense seasonal tourism, exacerbates the imbalance between water supply and demand. In this context, reclaimed water has become an essential strategic resource—particularly in coastal areas where secondary-treated effluents are still discharged directly to the sea. Reclaimed water is more cost-effective than desalination, alleviates pressure on overused freshwater bodies, and provides valuable nutrients that can partially substitute synthetic fertilisers.

Yet without proper nutrient management, these benefits can quickly turn into environmental risks. Farmers commonly continue applying conventional fertiliser rates, disregarding the nutrient load already present in reclaimed water. This leads to nutrient surpluses, soil degradation, and eutrophication risks in both surface and groundwater bodies. These unintended impacts illustrate precisely the type of cross-sectoral trade-offs that the WEFE Nexus approach aims to prevent, highlighting the need for integrated tools and governance frameworks to ensure the safe and sustainable reuse of reclaimed water in agriculture.

Beyond water and nutrient efficiency gains, the demonstrator also delivered measurable energy and climate benefits, reinforcing its WEFE Nexus value. By optimising fertiliser application and avoiding unnecessary mineral inputs, the RICHWATER© tool reduced the embedded energy demand associated with fertiliser production, transport, and application. Based on the modelled reductions in fertiliser use achieved in the Axarquía Living Lab, this translates into estimated savings of approximately 883 kWh per hectare per year and an associated reduction of 0.26 tonnes of CO₂-equivalent emissions per hectare per year. These results demonstrate that nutrient management in reclaimed water irrigation is not only an agronomic and environmental measure, but also a tangible contribution to energy efficiency and climate mitigation, strengthening the overall WEFE Nexus performance of the intervention.

To address the above mentioned challenges, the BONEX Demonstration Project introduced the RICHWATER© nutrient management tool, which helps farmers optimise fertilisation based on the nutrient content of reclaimed water. Building on insights gained during BONEX co-creation activities with stakeholders, the tool was engineered to respond to the needs of farmers who increasingly rely on reclaimed water due to Axarquía’s severe water scarcity. Key functionalities include:

• Estimating the proportion of crop nutrient needs covered by reclaimed water (N, P, K and micronutrients).
• Calculating the remaining fertiliser requirements, avoiding excessive or unnecessary applications.
• Identifying the most cost-effective fertiliser combination, using a database of commercial products commonly used in the region.
• Reducing the risk of diffuse pollution, soil degradation, and nutrient leaching—critical environmental concerns in Axarquía’s fragile ecosystems.

The project lasted 40 months and followed a sequenced set of actions to integrate participatory approaches with Nexus perspective: The regional government had initially focused on the Water dimension by adopting supply-side policies—particularly the upgrading of wastewater treatment plants to increase the availability of reclaimed water. While essential, these measures considered reclaimed water mainly as an additional supply source, without assessing their implications for Energy use, Food production, or Ecosystem health. In the first stages of the project (M1 – M12), BONEX applied its WEFE Nexus Bridging Framework as a first analytical step to understand these cross-dimensional implications and identify potential trade-offs.

Through the BONEX workshops, stakeholders explored how reclaimed water, although beneficial for Food production due to its nutrient content, also carried Ecosystem risks if nutrients were mismanaged, potentially contributing to soil degradation and eutrophication. They also recognised that reducing fertiliser use through proper nutrient management could mitigate part of the Energy demand embedded in the production and transport of synthetic fertilisers. This participatory process served to integrate the ecosystem and energy dimensions which were largely absent from initial supply-focused discussions—and to identify end-user knowledge and capacity needs.

Informed by these insights, the project designed and oriented digital solutions such as the RICHWATER© tool to support decisions across all four Nexus dimensions (M13 – 30). The tool was crafted not only to optimise Water use, but also to reduce unnecessary Energy inputs such as those linked to the production of chemical fertilisers, support sustainable Food production, and protect Ecosystems by preventing nutrient surpluses. By addressing knowledge gaps and ensuring stakeholder co-creation through the workshops, BONEX completed a transition from a narrow water-supply perspective to a holistic WEFE Nexus implementation pathway that recognises the interdependencies between water availability, energy costs, agricultural productivity, and environmental protection.

In its final stage (M30–M40), the project consolidated these findings into a strategic plan for widespread reclaimed water implementation in Axarquía: the Nexus Bridging Plan (NBP). This plan outlines a comprehensive, long-term strategy for scaling reclaimed water use with a Nexus perspective. It promotes the deployment of digital nutrient management tools like RICHWATER© alongside complementary interventions such as water-efficient irrigation technologies, water-resilient crops, agroecological practices, capacity building, and farmer training programmes. Together, these measures form an integrated portfolio of solutions designed to support the long-term goals of strengthening water security, reducing environmental impacts, supporting sustainable food production, and lowering the energy demands of agriculture in the region.

The BONEX demonstrator in Axarquía combined field experimentation, digital innovation, and a structured WEFE Nexus participatory process to validate the RICHWATER tool and ensure its effective, sustainable adoption. Actions followed a deliberate sequence that linked technical development, stakeholder engagement, and environmental risk mitigation:

1. Development of the RICHWATER© digital nutrient management tool

A central activity of the demonstrator was the co-development of the RICHWATER© digital application by BIOAZUL and Smart-Logger. This tool was specifically designed to help farmers calculate precise fertiliser dosages when irrigating with reclaimed water, ensuring both agronomic efficiency and environmental protection.

This technical development ensured that reclaimed water—which contains valuable nutrients—could be used as an asset rather than an environmental liability, provided that nutrient inputs are properly managed.

2. Installation of tertiary treatment and establishment of the BONEX experimental site

BIOAZUL installed a tertiary treatment system at the Algarrobo WWTP to generate reclaimed water suitable for irrigation. This infrastructure, referenced in the DP description, allowed continuous monitoring of water quality, particularly nutrient content, salinity, and microbiological indicators.

The BONEX experimental site consisted of multiple plots planted with different varieties of mango and avocado, the region’s dominant subtropical crops. These plots were irrigated using controlled mixtures of tertiary-treated reclaimed water and groundwater, reflecting real irrigation strategies in Axarquía.

Continuous monitoring at this site produced the datasets needed to calibrate, refine, and validate the RICHWATER tool.

3. Field trials with blended reclaimed water and fertiliser adjustment

To evaluate both crop performance and environmental safety, crops were irrigated with different reclaimed water–well water mixing ratios. This approach allowed BONEX to study:

• nutrient delivery under varying reclaimed water concentrations,
• crop responses under different salinity and nutrient regimes,
• and implications for optimising fertiliser strategies.

Throughout the trials, BIOAZUL and Smart-Logger adjusted fertiliser dosages, comparing conventional practices with the tool’s recommendations. This process validated the tool’s capacity to prevent overfertilisation and demonstrated its agronomic and economic benefits.

4. Implementation of the BONEX WEFE Nexus Bridging Framework (WEFEF)

In parallel to technical experimentation, BONEX implemented the WEFEF Nexus methodology for participatory strategic planning to ensure that the demonstrator addressed system-wide challenges, not only water-supply deficits. This process helped stakeholders identify:

• environmental risks linked to reclaimed water (nutrient excesses, salinity),
• cross-sectoral dependencies between water, energy, food production, and ecosystems,
• and governance bottlenecks affecting reclaimed water adoption.

The WEFEF approach ensured that environmental impacts—typically overshadowed by the urgency to expand water availability—were incorporated into decision-making.

5. Participatory workshops with more than 100 stakeholders

A series of three participatory workshops, complemented by interviews and consultations, brought together over 100 stakeholders representing irrigation communities and cooperatives, farmers and cooperatives, local municipalities and regional authorities, water operators, private sector and research institutions.

Participants used tools such as Causal Loop Diagrams to identify problem drivers and reveal WEFE trade-offs. They co-created the functionalities of the RICHWATER© tool, discussed reclaimed water risks, and helped define viable implementation pathways—ensuring the tool responds not only to agronomic needs but also to governance and behavioural realities.

The development and application of the RICHWATER tool has been one of the central achievements of the BONEX project in the Spanish demonstrator. Designed to support reclaimed water irrigation, the tool is applicable to any crop type, but its greatest value is in optimising nutrient management for water-intensive subtropical crops, particularly avocados and mangoes, which dominate agricultural production in Axarquía. By calculating the nutrients already supplied through reclaimed water and adjusting fertiliser requirements accordingly, the tool allows farmers to significantly reduce their reliance on synthetic fertilisers, generating both economic savings and environmental benefits.

To assess its agronomic and economic performance, BONEX modelled the tool’s impact for four crops cultivated in the Living Lab—avocado, mango, passion fruit, and dragon fruit—using real nutrient concentration data from reclaimed water produced at the Algarrobo WWTP. These simulations enabled a precise estimation of the fertiliser savings achievable when adopting RICHWATER’s optimised dosing recommendations. In the case of young mango and avocado plantations, the tool delivered striking results: fertiliser use decreased by 68% and 79%, respectively. At farm scale, the application of the RICHWATER© tool on a 2.4-hectare Osteen mango plot in the Axarquía region demonstrated a reduction in fertilisation costs, equivalent to €2,163 per growing season (approximately €901 per hectare). These savings were achieved by adjusting mineral fertiliser doses according to the nutrients already supplied by reclaimed water, while maintaining crop nutritional balance and agronomic efficiency. Together, these results confirm that nutrient management tools such as RICHWATER© simultaneously deliver economic savings (Food), energy efficiency and emissions reduction (Energy), and lower risks of nutrient pollution (Ecosystems), thereby strengthening the overall sustainability of reclaimed water reuse within a WEFE Nexus approach.

Beyond water and nutrient efficiency gains, the demonstrator also delivered measurable energy and climate benefits, reinforcing its WEFE Nexus value. By optimising fertiliser application and avoiding unnecessary mineral inputs, the RICHWATER© tool reduced the embedded energy demand associated with fertiliser production, transport, and application. Based on the modelled reductions in fertiliser use achieved in the Axarquía Living Lab, this translates into estimated savings of approximately 883 kWh per hectare per year and an associated reduction of 0.26 tonnes of CO₂-equivalent emissions per hectare per year. These results demonstrate that nutrient management in reclaimed water irrigation is not only an agronomic and environmental measure, but also a tangible contribution to energy efficiency and climate mitigation, strengthening the overall WEFE Nexus performance of the intervention.

Beyond demonstrating the tool’s technical and economic value, BONEX worked closely with stakeholders to ensure its practical adoption within a broader water-reuse strategy. Through the participatory WEFE Nexus process, stakeholders jointly identified the institutional, behavioural, and capacity-related conditions necessary to scale reclaimed water use safely and sustainably. These insights were synthesised into the Nexus Bridging Plan (NBP), which now guides regional implementation. The plan outlines clear, actionable pathways, including:

• prioritising agricultural technicians and cooperatives as primary users and intermediaries;
• strengthening training programmes and digital capacity-building for farmers and advisors;
• deploying accessible business models such as tiered pricing, free demos, and cooperative subscriptions;
• ensuring alignment with regulatory frameworks such as the EU Water Reuse Regulation and the Nitrates Directive; and
• enabling offline functionality to accommodate rural areas with limited connectivity.

Together, these measures position RICHWATER© not only as a digital tool, but as a cornerstone of a comprehensive Nexus-aligned strategy to promote safe, efficient, and environmentally responsible reclaimed water reuse in Axarquía.

The BONEX demonstrator in Axarquía has shown that the effective implementation of a WEFE Nexus approach requires not only technological solutions, but also a rethinking of how users, institutions, and knowledge systems interact. The deployment and validation of the RICHWATER© tool revealed several key lessons. First, successful adoption hinges on engaging the right primary users: agricultural technicians, cooperatives, and irrigation community managers—actors who routinely advise farmers and manage water distribution. While farmers benefit directly from the tool, these intermediaries are better positioned to drive adoption and ensure correct application. Second, the demonstrator highlighted persistent barriers to reclaimed water uptake, such as salinity concerns, water-quality variability, and a general lack of nutrient literacy, all of which can undermine trust and lead to suboptimal fertilisation practices. Third, digital solutions must be intuitive, user-friendly, and aligned with regulatory requirements, including the Nitrates Directive and the EU Water Reuse Regulation, if they are to become part of daily agricultural decision-making. Finally, the WEFE Nexus framing proved essential for helping stakeholders move beyond a narrow focus on expanding water supply, and instead recognise the complex interdependencies between nutrient management, energy use, ecosystem protection, and food system resilience.

These insights underscore the high replicability potential of the RICHWATER© approach. The tool is particularly relevant for Mediterranean regions experiencing rapid expansion of reclaimed water use—such as Murcia, the Algarve, Cyprus, Israel, or Tunisia—where water scarcity is acute and nutrient-rich effluents are increasingly integrated into irrigation. Replication requires minimal adjustments, mainly in adapting nutrient profiles, crop requirements, and local regulatory thresholds.

The demonstrator also revealed strong scalability potential within Axarquía and across Andalusia. Irrigation communities and cooperatives offer clear channels to scale the tool, particularly when supported by the implementation pathways defined in the Nexus Bridging Plan: tiered pricing models that accommodate different farm sizes; public-sector endorsement to build trust and legitimacy; integration with EU compliance modules; and alignment with sustainability certification schemes that reward efficient nutrient management. Moreover, the tool fits naturally within Andalusia’s broader strategies for digitalising water, energy, and agriculture, and could be incorporated into emerging digital twin initiatives, providing real-time, Nexus-aware decision support at regional scale.

Together, these elements demonstrate that RICHWATER© is not simply a digital tool, but a transferable and scalable component of a holistic WEFE Nexus strategy for sustainable reclaimed water reuse across Mediterranean agriculture.