ObjectiveThe lack of a validated and cross-culturally equivalent scale for measuring individual-level water insecurity has prevented identification of those most vulnerable to it. Therefore, we developed the 12-item Individual Water InSecurity Experiences (IWISE) Scale to comparably measure individual experiences with access, use, and stability (reliability) of water. Here, we examine the reliability, cross-country equivalence, and cross-country and within-country validity of the scale in a cross-sectional sample.MethodsIWISE items were implemented by the Gallup World Poll among nationally representative samples of 43 970 adults (>15 y) in 31 low-income and middle-income countries (LMICs). Internal consistency was assessed with Cronbach’s alpha. Equivalence was tested using multigroup confirmatory factor analysis (MGCFA), the alignment method, and item response theory. Cross-country validity was assessed by regressing mean national IWISE scores on measures of economic, social, and water infrastructure development. Within-country validity was tested with logistic regression models of dissatisfaction with local water quality by IWISE score and regressing individual IWISE scores on per capita household income and difficulty getting by on current income.FindingsInternal consistency was high; Cronbach’s alpha was ≥0.89 in all countries. Goodness-of-fit statistics from MGCFA, the proportion of equivalent item thresholds and loadings in the alignment models, and Rasch output indicated equivalence across countries. Validity across countries was also established; country mean IWISE scores were negatively associated with gross domestic product and percentage of the population with access to basic water services, but positively associated with fertility rate. Validity within countries was also demonstrated; individuals’ IWISE scores were positively associated with greater odds of dissatisfaction with water quality and negatively associated with lower financial standing.ConclusionsThe IWISE Scale provides an equivalent measure of individual experiences with water access and use across LMICs. It will be useful for establishing and tracking changes in the prevalence of water insecurity and identifying groups who have been ‘left behind’.

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