This project had two main aims: (1) to identify surface water and groundwater that is exceeding, or is likely to exceed, 50 mg l−1 nitrate with agricultural input as a significant source; (2) to identify the parcels of land that drain to these waters. The work brings together and develops the nitrates review methods for surface water and groundwater, and is focused on providing the underpinning evidence for both the Nitrates Directive 2006 review and the requirements of the Water Framework Directive (WFD). The work was conducted within the Environment Agency of England and Wales in three phases: national-scale risk assessment and source attribution; local expert elicitation, source attribution and delineation of Nitrate Vulnerable Zones (NVZs) boundaries; national-scale quality assurance of the outputs. This paper gives an overview of all three phases of the project but focuses on the second phase, comprising the groundwater section of the work. This has been one of the most rewarding parts of the project, as it is the phase that brings a national-scale risk assessment down to a local scale and transfers ownership of risk assessment to the local hydrogeological experts within the Environment Agency. It is also a critical phase in helping to ensure that the measures are targeted as accurately as possible.