Importance of Holistic Stormwater Management in Safeguarding Europe's Water Reserves

According to the latest U.N. report, 2 billion people or 26% of the world's population lack access to safe drinking water. Recent data from World Resources Institute reveal an even more alarming view: roughly 4 billion people are exposed to water stress at least one month per year. This paper examines the little-discussed links between the increasing water stress, natural water cycle disturbances and the insufficient adoption of sustainable stormwater management practices. The second part of the paper also offers an insight into some promising case studies across Europe, showing how holistic stormwater management solutions can relieve water scarcity, mitigate flood risks and preserve biological diversity while ensuring long-term economic benefits.

_{Increasing Use and Declining Reserves: Water Stress in Europe}

While the Middle East and North Africa are seen as the world's most water-stressed regions, the current water consumption trends and policies, coupled with unexpectedly severe droughts witnessed in the last few years, mean that water scarcity has become a global issue. Growing populations, increasing urbanization, developing industries and agriculture, as well as climate change have all contributed to water management culture that is unsustainable in the long term.

Historically, most of Europe has had adequate water reserves to sustain its populations while meeting industrial and agricultural needs. In fact, an average person in Europe consumes 144 liters of water per day. While the figure might be staggering, household use actually accounts for just 12% of Europe's annual water consumption, with agriculture taking 40%, energy production 28%, and mining and manufacturing 18%.

In light of increasing droughts over the past years, Europe's generous water use habits now require reevaluation and optimization across all sectors. The continent has been facing annual droughts since 2018, while 2022 was recorded as the driest in at least 500 years.

Recent analyses of satellite data indicate a steady depletion of Europe's aquifers already since the start of the 21^st century — with estimates of nearly 84 gigatons of water lost per year. Extreme heatwaves and prolonged periods without rain across the continent have resulted in increased groundwater extraction and aquifer depletion to meet Europe's unsustainable water consumption patterns.

_{Are Current Measures Enough: Call for a Water Resilience Strategy}

While lauded as one of the world's leading regions regarding decarbonization, the EU has lately been criticized for not preventing and even funding unsustainable use of water resources.

The European Court of Auditors issued a report already in 2021 concluding that the current EU funding conditions for irrigation projects do not safeguard against unsustainable water use. In the autumn of 2023, Living Rivers Europe, a coalition of six environmental organizations, published a paper calling on the EU to stop subsidizing activities harmful to river morphology, water quality, natural water retention and groundwater.

Despite the growing concerns among Europe's environmental organizations and water services providers, the bloc's long-awaited water resilience plan has been put on hold with no postponement reason offered by the EC.

_{Looking for the Way Out: Alternative Water Sources and Causes of Water Scarcity}

With Europe's freshwater reserves on the decline, alternative water-sourcing technologies such as desalination and wastewater reuse have been gaining traction, particularly in the most drought-affected countries.

For example, Spain last spring announced allocating 2.2 billion euros for drought response measures, with more than half of this sum planned for wastewater treatment and reuse infrastructure and constructing new desalination plants.

Furthermore, the EU's Urban Wastewater Treatment Directive, enforced in the Member States last spring, is setting a united standard across the bloc for water reuse in agriculture.

Both desalination and wastewater reuse are clearly needed to address the EU's growing water consumption; however, these technologies remain cost- and energy-intensive, making their swift implementation challenging. Both require careful monitoring to minimize pollution risks in the local ecosystems.

Furthermore, neither desalination nor wastewater reuse sufficiently addresses natural water cycle disruptions — a major factor affecting declining freshwater reserves worldwide.

Both wind patterns and increased reliance on conventional drainage systems contribute to the extracted water being returned to the environment, sometimes hundreds or even thousands of kilometers from its source, failing to replenish local groundwater reserves and setting the stage for even more acute water stress in the future.

_{Stormwater Management Inspired by Nature: Exploring the Potential of Water Retention and Reuse}

Preserving and restoring Europe's natural water retention landscapes is integral to restoring the water cycle and reducing vulnerability to both droughts and flooding. Examples of such landscapes include swamps, marshes, bogs, lake systems, floodplains, and other wetlands that can store large volumes of rainwater, slowly releasing it over time.

It is less known that the processes of stormwater local retention and/or subsequent infiltration observed in nature can also be successfully applied to urban or agricultural settings.

Such systems purify rainwater to be gradually infiltrated or stored and reused for various non-potable purposes, reducing the need for groundwater depletion.

While EU-wide legislation stipulating local stormwater management is still lacking, some member states have taken matters into their own hands. For example, the Czech Republic has passed a law that requires new and reconstructed buildings and sealed surfaces to be equipped with a local rainwater management system to obtain a completion certificate. If local hydrogeological conditions and pre-existing infrastructure allow for it, the preferred disposal method for excess water is local infiltration ensuring replenishment of underground water resources along with increasing water evaporation at the site of installation.

Germany has also already introduced its own holistic national water strategy that includes measures such as restoring forests and green spaces, regulating water distribution in case of shortages and introducing water-saving incentives. 

_{A New Take on Irrigation and Agricultural Drainage}

In Europe's southernmost areas like Crete, water abstraction for agriculture can reach even 85% of the total consumption. Increasing the cultivation of drought-resistant crops adapted to the local climate and adopting precision irrigation technologies must be implemented alongside increased wastewater reuse to ensure food security and preserve dwindling water sources.

However, in central and northern Europe, rainwater harvesting and reuse has the potential to become a viable complementary measure. In 2022, the research institutes Vertify and Deltares, together with the University of Wageningen and piping system manufacturer Pipelife Netherlands, started a pilot "Freshwater Farmers." The 4-year project explores how current agricultural practices could be adapted to protect crops from extended droughts and increasing salinization.

Historically, the flood-prone coastal areas in the Netherlands have been drained by placing horizontal drainage pipes in the soil and diverting the excess water to a ditch from where it flows into the sea. However, coupled with increasing water consumption and more frequent dry periods, the practice has led to soil salinization in several coastal areas.

As part of the pilot, a traditional drainage system in an 8-acre potato field in North Holland was turned into a closed network for harvesting the surplus precipitation during winter and storing it for the dryer summer months. An automated water-level control system was installed in the collector wells, allowing the farmer to control the groundwater levels in the field as needed.

While the study is set to continue for another season, the initial results are promising. The closed drainage system has been found not only to ensure optimal water supply for the plants throughout the growing season but also to prevent saltwater from seeping into the land and minimize the nutrient losses from the soil. The researchers believe that it would be possible for such systems to pay off in just five years, making them an attractive investment to farmers. 

_{Large-Scale Rainwater Infiltration and Reuse System in Action}

Local stormwater management systems can be equally suitable for a family garden or a multi-hectare industrial complex. A project of the latter kind was recently completed in Gromadka municipality, Southern Poland. A 17-hectare stormwater management system was designed and built for an upcoming production site expected to be completed in the first quarter of 2024. The comprehensive solution boasts two water retention tanks with volumes of 1100 m³ and 50 m³ that allow rainwater to be stored for the plant's production purposes.

In addition, three underground infiltration fields have been installed across the plant's territory with a combined volume of 3024 m³. Both systems are interconnected and equipped with an automated monitoring system that continuously measures the water levels and remaining volume in the tanks.

Thanks to the local stormwater management and reuse system, the production site is not only well protected from flood damage but also supports healthy water balance within the vicinity due to rainwater infiltration. The system is also feasible economically, offering reduced water consumption costs due to water reuse and eliminating costs associated with discharging rainwater into the municipal sewage network.

_{Preserving Healthy Water Resources for Next Generations}

As Europe faces the pressing issue of water scarcity, adopting holistic strategies and sustainable water management practices is crucial to secure the future of this precious resource.

While addressing water losses in supply networks, optimizing water-intensive industries and processes, and embracing new water-sourcing technologies all remain necessary to tackle the growing water demand, a more holistic approach to water resilience is also needed — focusing on preserving and restoring the natural water cycle and replenishing the groundwater levels to ensure a future with sufficient water resources available for everyone.