Hard Water and IBDInflammatory bowel disease (IBD), encompassing Crohn’s disease and ulcerative colitis, is influenced by both genetic predisposition and environmental factors. Study Design and Water Exposure AnalysisResearchers conducted a cross-sectional and prospective cohort study including 481,468 adults. Logistic regression models examined the association between hard water exposure and IBD prevalence at baseline, while Cox regression models assessed incident disease risk during a mean follow-up of 14.6 years. Notably, individuals with low genetic risk for Crohn’s disease experienced a stronger protective effect from very hard water exposure (HR: 0.74; 95% CI: 0.57–0.95), suggesting a gene–environment interaction. ConclusionThese findings suggest that hard water exposure may have a protective role in Crohn’s disease prevention, particularly among individuals at lower genetic risk.