By the Agricultural University of Athens (AUA), partner of the GEORGIA project.
Across Europe and beyond, agriculture is facing a new water reality. Rainfall is becoming less predictable, droughts are becoming more frequent, and pressure on freshwater resources is increasing. For many farming regions, relying only on conventional freshwater irrigation is no longer enough. A more resilient agricultural future will require a broader water toolbox, one that includes not only groundwater and surface water, but also rainwater, treated wastewater, atmospheric water, saltwater-based systems, industrial effluents, and recovered organic nutrients. These resources, when carefully treated, monitored, and managed, can help farmers reduce water stress while supporting more circular and sustainable food production.
Why non-conventional water matters
Water scarcity is not just an environmental issue. It directly affects food security, farm productivity, soil health, and rural economies. In areas where freshwater is limited, farmers may face difficult decisions: reduce irrigation, change crops, increase pumping from groundwater, or invest in alternative sources. Non-conventional water resources offer another path. They can help agriculture reduce pressure on freshwater reserves, increase resilience during drought periods, reuse resources that would otherwise be lost, recover nutrients from waste streams, support local and decentralized water solutions.
The idea is simple: instead of treating water, nutrients, and organic residues as waste, we can redesign agricultural systems so that these resources are reused safely and efficiently.
Rainwater: capturing a seasonal resource
Rainwater harvesting is one of the oldest and most intuitive water management practices. In modern agriculture, it can be combined with storage tanks, ponds, reservoirs, soil-water retention measures, and digital monitoring systems. Collected rainwater can be used during dry periods, reducing dependence on groundwater or public water networks. In some cases, rainwater harvesting can also reduce runoff and erosion, especially when combined with landscape-level Nature-Based Solutions such as vegetated buffer strips, swales, terraces, or retention basins. The challenge is that rainwater is seasonal. Storage capacity, catchment design, evaporation losses, and irrigation demand must all be carefully considered. A rainwater system is only useful if it is designed according to the local climate, crop needs, and farm infrastructure.
Treated wastewater: turning waste into a resource
Treated wastewater is one of the most promising alternative water sources for agriculture. When properly treated and monitored, it can provide a stable irrigation source, especially in regions where freshwater is scarce. It may also contain nutrients such as nitrogen and phosphorus, which can partially reduce the need for synthetic fertilizers. This creates an opportunity for both water reuse and nutrient circularity. However, wastewater reuse must be managed carefully. Water quality, salinity, pathogens, heavy metals, emerging contaminants, and regulatory requirements are all critical factors. Farmers also need clear guidance on which crops are suitable, what irrigation methods should be used, and how soil and groundwater can be protected. For this reason, treated wastewater reuse is not simply a water supply solution. It is a complete management system that requires monitoring, trust, technical expertise, and strong governance.
Atmospheric water: harvesting humidity from the air
Atmospheric water harvesting explores a different idea: capturing water directly from humidity, fog, dew, or condensation. In some climates, passive systems can collect dew using radiative cooling surfaces, while active systems can condense water using energy-powered cooling technologies. These solutions are especially interesting for remote or water-scarce areas, where conventional water infrastructure is limited. Atmospheric water is not usually a replacement for full-scale irrigation, especially for water-demanding crops. But it can provide supplementary water for seedlings, high-value crops, greenhouses, or small-scale applications. Its success depends strongly on local humidity, temperature, energy availability, material costs, and maintenance needs.
Saltwater and brackish water: working with salinity
In many coastal and arid regions, saltwater intrusion and brackish groundwater are growing problems. Instead of ignoring these resources, new approaches are exploring how they can be used safely. One pathway is desalination, which can produce freshwater from saline or brackish water. Another pathway is the use of salt-tolerant crops or halophytes in controlled systems, where saline water can support biomass production while contributing to circular water management. Nature-Based Solutions can also play a role by using vegetation, wetlands, or biofiltration systems to manage saline or nutrient-rich water streams. Still, salinity remains a major risk. Poorly managed saline irrigation can damage soil structure, reduce crop productivity, and create long-term degradation. Any use of saltwater or brackish water must therefore be supported by soil salinity monitoring, drainage management, and crop-specific thresholds.
Groundwater: a resource under pressure
Groundwater remains essential for agriculture in many regions, but over-extraction can lead to declining water tables, higher pumping costs, salinization, and ecosystem damage. The goal is not necessarily to eliminate groundwater use, but to manage it more sustainably. This can include combining groundwater with rainwater, treated wastewater, or desalinated water; improving irrigation efficiency; monitoring aquifer conditions; and reducing unnecessary pumping. Groundwater should be treated as a strategic reserve, not an unlimited supply.
Organic nutrients and wastewater sludge
Water is not the only resource that can be reused. Agriculture also depends heavily on nutrients, especially nitrogen, phosphorus, and potassium. Recovering nutrients from organic sources can reduce dependence on synthetic fertilizers and support circular farming systems.
Potential sources include:
- treated wastewater sludge,
- composted organic residues,
- digestate,
- recovered phosphorus products,
- biochar-based amendments,
- sludge-derived soil conditioners.
When properly treated and certified, these materials can improve soil organic matter, water retention, and nutrient availability. They may also support degraded soils and reduce fertilizer costs. However, they must be used with care. Quality control is essential to avoid contamination risks, odour problems, nutrient imbalance, or public concern. Application rates, timing, crop type, soil properties, and regulatory limits all matter.
Nature-based solutions: designing with natural processes
Nature-Based Solutions are central to a more resilient water future. Instead of relying only on hard infrastructure, NBS use natural processes to retain, filter, store, or reuse water.
Examples include constructed wetlands for wastewater treatment, vegetated buffer zones for runoff reduction, retention ponds and infiltration basins, soil amendments that improve water holding capacity, reed beds for sludge drying, agroecological practices that improve soil structure, cover crops and mulching to reduce evaporation and erosion.
These systems can deliver multiple benefits at once: water treatment, nutrient recovery, biodiversity support, erosion control, carbon storage, and improved landscape resilience.
Their strength is that they do not address water scarcity as a single problem. They connect water, soil, biodiversity, climate adaptation, and farm productivity.
The barriers to adoption
Despite their promise, non-conventional water and NBS practices are not always easy to adopt. Farmers and local authorities often face mainly a combination of technical, economic and social barriers:
- Technical barriers: many systems require specific knowledge, monitoring, and maintenance. Farmers need to understand water quality, soil response, crop sensitivity, irrigation scheduling, and system performance. Lack of technical support can slow adoption.
- Economic barriers: initial investment costs can be high. Storage tanks, treatment systems, sensors, pumps, filters, and monitoring equipment may require financial support. Even when long-term benefits are clear, upfront costs can be difficult for farmers.
- Social barriers: public perception matters. Some consumers may have concerns about wastewater reuse or sludge-derived products, even when they are treated safely. Building trust requires transparency, certification, communication, and demonstration.
For these practices to become widely adopted, farmers need more than technology. They need an enabling environment. That means clear guidelines, reliable water quality data, affordable monitoring tools, training and advisory support, financial incentives, demonstration sites, simple decision-support systems, long-term policy stability. Most importantly, solutions must be adapted to local conditions. A practice that works in a greenhouse may not work in an open field. A system suitable for a humid region may fail in an arid island landscape. A water source suitable for one crop may be risky for another. There is no universal solution. The future lies in smart combinations.
Why this matters
The transition toward non-conventional water use is not only about saving water. It is about changing how agriculture understands resources. Wastewater can become irrigation water. Rainfall can be stored. Humidity can be harvested. Organic residues can return nutrients to the soil. Landscapes can be designed to retain water instead of losing it. This shift supports a more circular and resilient agricultural model, one where water, nutrients, soil, and technology work together.
Looking ahead
As climate pressures intensify, agriculture will need to move beyond conventional water thinking. Non-conventional water resources and Nature-Based Solutions offer a practical pathway toward farms that are better prepared for drought, more efficient in resource use, and more connected to local ecosystems. The challenge now is to move from promising examples to wider implementation. That means understanding what works, where it works, what it costs, and what support farmers need to adopt it. The future of irrigation will not depend on one single water source. It will depend on the ability to combine multiple resources safely, intelligently, and sustainably. Every drop has value. The next step is learning how to use each one wisely.
Explore the GEORGIA factsheets on Oplossingen voor wateroptimalisatie to discover practical approaches, technologies, and Nature-Based Solutions that support sustainable water management in agriculture.
