Water retention covers a wide set of mechanisms (see synthesis document n°1) the effect of which are to increase the capture of water by aquifers, soil, and aquatic and water dependent ecosystems.
More precisely it refers to capabilities of catchments (including wetlands, rivers and floodplains but also other land areas) to hold or retain as much water as possible during periods of abundant or even excessive precipitation, so that water is available for use during dry periods and runoff peaks are minimized.

Within the framework of natural water retention measures (NWRM), urban planning refers to the application of the "Grey to Green" principle within cities. The specific focus of urban planning for NWRM is to achieve sustainable water management by mimicking natural functions and processes in the urban environment.

Wetlands restoration and creation can involve: technical, spatially large-scale measures (including the installation of ditches for rewetting or the cutback of dykes to enable flooding); technical small-scale measures such as clearing trees; as well as changes in land-use and agricultural measures, such as adapting cultivation practices in wetland areas.ﾠ Wetland restoration can improve the hydrological regime of degraded wetlands and generally enhance habitat quality. (Creating artificial or constructed wetlands in urban areas can also contribute to flood attenuation, water quality improvement and habitat and landscape enhancement).
- Based on Stella definitions, adapted by NWRM project experts and validated by the European Commission