This study identifies multiple pathways connecting household water insecurity with child nutrition. Using nationally representative samples for 18 countries, we examine the mediating role of child's dietary diversity as a function of household water status, while also accounting for sanitation. We construct a latent household water insecurity score (HWI) and use Structural Equation approach to model underlying pathways. HWI affected child's HAZ score and hemoglobin both directly and indirectly, with a mediation from child feeding alongside effects from sanitation. Broadening the conception of household water insecurity and accommodating the indirect effects of water could improve explanations of child under-nutrition.