Potential uses of pumped urban groundwater. A case study in Sant Adrià del Besòs (Spain)

Urban groundwater has been over-exploited during the past, mainly for industrial uses, and it now tends to be reduced or abandoned due to pollution and/or changes in land use. The use and the subsequent disuse of groundwater resulted in rising water tables that damage underground structures (e.g., building basements and underground car parks and tunnels), leading to additional pumping in urban areas. This is the case of the underground parking lot of Sant Adrià del Besòs (NE Spain), where large amounts of urban groundwater are pumped to avoid seepage problems. The question that arises here is if this pumped groundwater can be used for other purposes (e.g., drinking water and urban irrigation) instead of wasting this valuable resource. To answer this question, it is necessary to quantify the groundwater recharge and to assess the evolution of ground-water quality in order to properly identify its potential uses. The limiting factor to define the uses of this resource is the groundwater quality because ammonium and some metals (iron and manganese) are present at high concentrations. Hence, further treatment would be needed to meet drinking water requirements. The pumped groundwater could also be used for supplying the ecological river flow and/or for mitigating seawater intrusion problems. Currently, only a small amount of this urban groundwater is used for cleaning public areas and watering public gardens. This situation highlighted the urgent need to manage this resource in a responsible and more efficient manner, especially in moments of high water demand such as drought periods.