Background According to the current analysis of future climate trends, some European regions will suffer a dramatic reduction in the availability of freshwater. Artificial Aquifer Recharge (AR), aimed at counterbalancing natural water losses, is an appropriate and effective tool to diminish the depletion of freshwater and groundwater. Presently, Italian water directives have limited its application to salty aquifers, and accordingly AR techniques have already been applied to coastal salty aquifers to combat salt intrusion, and to a few tests to assess the possibility of recharging depleted aquifers. If not regulated and properly applied, large-scale use of AR could pose risks for both the quality (e.g. pollution) and the distribution of freshwater (e.g. changes in the dynamic of the aquifer). To guarantee the correct application of recharge techniques, at least the following points should be regulated by proper legislation: location and procedures to extract water resources; the chemical and physical characteristics of recharge water; the properties and the hydrogeological structure of the aquifer; recharge methods; and the environmental impact; design and set-up of the monitoring system. Objectives The objective of the WARBO project was to provide the basic technical knowledge for the development of regulations for Aquifer Recharge (AR), and to provide tools to protect and enhance water and water-related ecosystems. The project focused on demonstration sites hosting ecosystems of Community interest, where urgent measures are needed to combat water scarcity. Specifically, the project aimed to develop protocols for the management of recharge activities, by the application of several direct and indirect investigation and monitoring methodologies. Results The WARBO project tested Artificial Aquifer Recharge (AR), also known as Managed Aquifer Recharge (MAR), with different approaches in three different flood plain areas representative of European geo-morphological contexts, typical of different climatic regions of Central and South Europe, taking into account the problems arising from long periods of drought and/or heavy rainfall, and where the protection of aquatic ecosystems is also a key factor. The project’s test sites were located in two main areas: two in the high Friuli Plain (north-eastern Italy) and one in the Po Valley. In the first area, one site was in the industrial zone of Ponte Rosso (Pordenone province), where a wetland receives treated industrial wastewater, and the other was in Mereto di Tomba (Udine province) and involved an innovative experimental facility for artificial recharge. In the second area, the Quarry Lake of Ponte San Pietro Copparo (Ferrara province) was chosen for the availability of a plant for aquifer artificial recharge. The project developed a protocol defining the best procedures for the implementation of MAR in these very different hydrogeological and environmental conditions. Analytical procedures were used to characterise the sites, to identify the causes of aquifer deterioration, to assess the quality and quantity of surface water, and to develop a panel of possible solutions for the recovery of surface and ground water bodies with high cost/benefit ratios. Well-known methodologies (e.g. GIS database and data mapping, biological and geological monitoring) and innovative ones were used, the latter including isotopic analysis of precipitation, study of surface and groundwater using laser absorption spectroscopy to assess water quality; and co-focal microRaman to characterise minerals in the rocks lining surface feeder reservoirs and aquifers. Ground-penetrating radar (GPR), Electrical Resistivity Tomography (ERT) in association with Thermal Analysis and Passive Seismic techniques were also used to analyse underground structures. Subsurface conceptual models were elaborated using a multi-disciplinary hydrogeological and geochemical approach. The project team also monitored and modelled seepage dynamics, which enables aquifers unsuitable for recharge to be identified. Quantitative and qualitative improvements in groundwater were verified, not only during periods of water surplus but also in times of water shortage. As a result of the project’s analysis, protocols were elaborated to support the management of aquifer recharge. Cost/benefit analysis was done at each of the three test sites. From this, the project team concluded that MAR feasibility is greater in water-stressed regions. Nevertheless, the project team also pointed out that even though MAR, per se, is not always economically attractive in certain situations, if applied together with other mitigation measures to decrease pollution load, vulnerability, and control and impact compensation, it can provide positive cost/benefit outcomes. WARBO established that abandoned excavations, pits and ponds can be easily transformed into MAR infrastructures. The test sites of Mereto and Copparo were abandoned water reservoirs and did not require any particular preparation for the AR activity. At Ponte Rosso site, the MAR infiltration basin helped to protect water resources from excess heavy metals and thermal pollution. The project also created a new phyto-remediation pond to treat grey water discharges to safeguard the biodiversity of a nearby wetland. The infiltration pond at the Mereto site increased recharge capacity, with a positive impact on water quality and a decreased risk of contamination from saltwater intrusion. The pond created at the Copparo site should improve water surface quality in a 4 ha lake, a major water source for migratory species where biodiversity improvements were recorded; the implementation of this MAR also included the creation of a connection between the lake and the channel network designed to be an expansion area during flooding. Small, isolated MAR structures, like those at the three test sites, already provide benefits at local scale; larger integrated MAR systems are required to achieve municipal or regional scale impacts. The project’s methodology complies and supports the implementation of the Water Framework Directive (2000/60/CE) and other EU directives and legislation dealing with water, including environmental quality standards (2008/105/EC) and the Groundwater Directive (2006/118/EC). Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).