The GEOSS Water Strategy–From Observations to Decisions (Lawford et al., 2014) identifies several key water variables as Essential Water Variables (EWVs). This was based on broad meta-surveys (Unninayar et al., 2010) of water-related observational needs for GEO Societal Benefit Aeas (SBAs) that included energy and agriculture among others. This paper summarizes currently defined EWVs required by key research and applications sectors involved in decision support within the Water-Energy-Food (WEF) Nexus. There is a notable overlap between the EWVs and a preliminary assessment of Essential WEF Variables. We also highlight EWVs that are relevant to the indicator monitoring objectives of the UN Sustainable Development Goals (SDGs), and GEOGLOWS priority thematic communities—especially those that overlap with the WEF Nexus. Besides primary EWVs such as precipitation, soil moisture, evapotranspiration and water levels/storage, supplemental EWVs are identified that support the integrated multi-sectoral information needed by WEF decision support applications. Examples of supplemental EWVs include surface meteorology and winds, solar radiation, land use/land cover and vegetation. Both Remote Sensing (RS) platforms and In-Situ observing networks are required to address the broad range of space/time resolutions, accuracies, and data latencies that end-users need. The AGU-2021 is invited to comment on, endorse and/or recommend additional EWVs that should be considered for adoption by GEOGLOWS and the GEO (Group on Earth Observations).