The intensifying competition for surface and groundwater resources is widely documented. The OECD Environmental Outlook to 2050 highlights that water resources are already over-used or over‐allocated in many places, with global demand expected to increase by 55% between 2000 and mid-century. Groundwater withdrawals have risen sharply over the past years – increasing nearly tenfold according to some estimates. These pressures, projected to be further exacerbated by climate change, have already made water allocation an urgent issue in a number of countries and one that is rising on the agenda in many others. Within this context, the OECD published the report Water Resources Allocation: Sharing Risks and Opportunities in 2015 to strengthen the evidence base and develop policy guidance to improve the design of allocation regimes.

Building on this work, further analysis was undertaken to examine the specific challenges related to groundwater and how allocation arrangements can be designed in light of groundwater’s distinctive features. The analysis builds on a series of case studies to document groundwater allocation challenges in a variety of contexts and provides policy guidance to assess and enhance allocation regimes for groundwater.

This report is an output of the OECD Environment Directorate. It was prepared by Kathleen Dominique and Marit Hjort, with guidance and input from Xavier Leflaive. The case studies on groundwater allocation were prepared by Marit Hjort, with input from delegates of the OECD Working Party on Biodiversity, Water and Ecosystems and in-country experts, notably: P.G. Pedersen, Chief advisor, Unit of Water Resources, Agency for Water and Nature Management, Ministry of Environment and Food, Denmark; Dr. Sharon Megdal, Director, Water Resources Research Center, University of Arizona; Jiro Hiratsuka, Ministry of Environment, Japan and experts from the local government in Kumamoto City; Daniel Rivera, International Cooperation Management, National Water Commission of Mexico; Ana Fueyo and Dr.Alberto López-Asenjo Garcia, Ministry of Agriculture, Spain, José Ángel Rodríguez-Cabellos, Head of the Planning Office in Guadiana River Authority, Spain; Larry French, Director of Groundwater, Rima Petrossian, Manager of Groundwater Technical Assistance, and Kimberly Friesen Leggett, Media Relations Specialist, Texas Water Development Board, C. E. Williams, General Manager, Panhandle Groundwater Conservation District; Jérémy Devaux, French Ministry of the Environment, Energy and the Sea, Jean‐Daniel Rinaudo, Bureau de recherches géologiques et minières (BRGM), France, Floriane Di Franco, Permanent Assembly of Agricultural Chambers, France, Patrice Garin, member of the research collective Gestion de l’Eau, Acteurs, Usages, France; Dr. R.C. Jain, Former Chairman, Central Ground Water Board and Central Ground Water Authority, Ministry of Water Resources, River Development and Ganga Rejuvenation, Government of India.

The authors are also grateful to colleagues and experts who provided valuable comments on the report, including Simon Buckle, Guillaume Gruère, Paul O’Brien, Hannah Leckie (OECD Secretariat) and Ian Barker, of Water Policy International, Henry Leveson-Gower, DEFRA, UK and Professor Mike Young, University of Adelaide. Editorial support from Janine Treves and administrative support from Angèle N’Zinga are also gratefully acknowledged.