Achieving equitable access to water, sanitation and hygiene (WASH) services requires paying special attention to the most disadvantaged segments of the population. Yet, despite all the progress made to evaluate the access of vulnerable and marginalized groups, important knowledge gaps still remain with respect to identifying their specific barriers and needs. At the global level, for example, the two monitoring mechanisms for SDG 6 – the Joint Monitoring Programme (JMP) and Global Analysis and Assessment of Sanitation and drinking-water (GLAAS) – face difficulties in understanding how, and to what extent, vulnerable and marginalized groups access WASH services. In this context, this work examines the UNECE/WHO-Europe ‘Equitable Access Score-card' for assessing the access to WASH services by vulnerable and marginalized groups. In particular, we: (i) analyse its strengths and limitations as a tool for revealing the needs of these groups in accessing WASH services; and (ii) propose an extended variant of the score-card that addresses these limitations. We test this version in two local-level case studies: Lima (Peru) and Castelló de la Plana (Spain). The score-card diagnosis is found to be particularly useful for collecting information on the level of access of the different vulnerable and marginalized groups, as well as the specific public policies and funding mechanisms in place that address and support their needs. However, the score-card should be complemented with specific assessments of all five normative dimensions of the human rights to water and sanitation (access, availability, quality, acceptability and affordability) in order to have a better understanding of the concerns for service delivery for the different vulnerable and marginalized groups.