It is possible to assess the harm that society suffers from an anthropogenic event based on the impact of groundwater pollution on society. Indexing methodologies are commonly applied to assess the social vulnerability of aquifers. However, they assign weighting and rating values for the different factors involved, make them very subjective. This research proposes to assess the social vulnerability to groundwater pollution by considering three factors: the uses of groundwater resources, the exposed population, and the socio-economic losses. In order to eliminate the subjectivity of indexing methodologies, a K-means cluster analysis was used to assess the social vulnerability. Using this method, a social vulnerability map can be produced with greater objectivity. The proposed methodology was applied to an aquifer located in central Spain, an area with significant agricultural development. Low population density and unproductive zones result in low social vulnerability in most of the area. Nevertheless, high social vulnerability is observed in the southern regions due to agricultural development which leads to higher socio-economic variables and demand for groundwater resources for agricultural activities. Similarly, high social vulnerability is observed in the northeast, mainly influenced by groundwater use and exposed population. These results show that social vulnerability in most of the study area is not very significant for assessing the risk of groundwater contamination, because the damage to the social, environmental or economic sector is low. However, in the south and northeast in the study area, pesticides and fertilisers should be used with caution, as they significantly increase the risk of groundwater contamination and thus the impact on society. The K-means clustering method proved to be an objective and effective option for assessing social vulnerability to groundwater pollution in aquifers.