Given the intensifying water scarcity crisis and the increasing use of urban wastewater in the agricultural sector, farmers’ adherence to health-related practices has become crucial for protecting human health, environmental sustainability, and food security. The present study aimed to analyze the determinants of farmers’ health behaviors regarding the use of urban wastewater for irrigating agricultural crops in Kermanshah County, Iran. The theoretical framework of the study was based on the Health Belief Model (HBM). This research was applied in terms of purpose and descriptive-correlational in terms of methodology. The statistical population consisted of all farmers using urban wastewater for agricultural irrigation in Kermanshah County. Data were collected through a researcher-developed questionnaire. The validity of the instrument was confirmed by a panel of experts, and its reliability was verified using Cronbach’s alpha coefficient. Data were analyzed using SPSS software. The findings revealed that the constructs of the Health Belief Model explained 30.4% of the variance in farmers’ health behaviors. Furthermore, the results of regression analysis indicated that self-efficacy and perceived barriers had positive and statistically significant effects on farmers’ health behaviors. The findings suggest that enhancing farmers’ confidence in their ability to implement health-related practices and increasing their awareness of the challenges and risks associated with wastewater use can contribute to the improvement of health behaviors. Based on the results, it is recommended that educational and extension programs focus on strengthening farmers’ self-efficacy, improving practical skills, and increasing awareness of the health and environmental consequences of wastewater use. In addition, addressing structural factors and providing institutional support alongside educational interventions can play a significant role in promoting farmers’ health behaviors.