Background: Food insecurity and water insecurity are increasingly recognized as interconnected social determinants of health; however, their co-occurrence remains underexplored in U.S. populations. SNAP households with children experience a high prevalence of both food and water insecurity. This study estimated the prevalence of food insecurity and water insecurity and examined their co-occurrence among SNAP households with children in the Southern U.S. Methods: A cross-sectional, web-based survey was conducted among 683 SNAP participants residing in households with children. Food insecurity was assessed using the 10-item USDA Adult Food Security Survey Module, and water insecurity was measured using the Household Water Insecurity Experiences (HWISE) scale. Descriptive statistics estimated prevalence, and regression analyses assessed associations. Results: Food insecurity (75.1%) and water insecurity (53.9%) were highly prevalent among surveyed SNAP households with children. Nearly half of households (48.6%) experienced both conditions, while 19.6% were secure in both. Food insecurity alone was reported by 26.5% of households, and water insecurity alone by 5.3%. Higher food insecurity scores were associated with increased odds of water insecurity (AOR = 1.33, 95% CI: 1.26–1.40, p < 0.001). Conclusions: Food insecurity and water insecurity frequently co-occur among SNAP households with children. Integrated public health strategies addressing both food and water access are needed to reduce disparities and improve household well-being.