Untreated wastewater irrigation is a popular practice in developing countries, particularly those with poor wastewater treatment facilities. Whilst wastewater irrigation has harmful effects on the human health and the environment, little is known about knowledge and attitude regarding this source of water among farmers who use it as well as their reasons for irrigation using it. This cross-sectional survey study was conducted to explore knowledge and attitude of Iranian wastewater users towards this water resource. Also, their drivers for untreated wastewater irrigation were explored. Results indicated that farmers have a relatively high knowledge about the inappropriate quality of untreated wastewater and its negative effects. Although they were concerned about the health, environmental and social impacts of untreated wastewater, they believed that using this water resource is economically profitable for them. The Bayesian Network (BN) and Partial Least Squares (PLS) path modeling was used to clarify factors influencing attitude towards untreated wastewater irrigation. Analysis of the causal models specified that knowledge, moral norm and social cohesion significantly affects attitude towards untreated wastewater. Also, social cohesion moderated the effects of knowledge and subjective norm on attitude. The study clarified that the most important drivers for using untreated wastewater for irrigation by farmers were water scarcity, increasing crop yield, decreasing production costs, difficulty to access freshwater, saving freshwater and increasing soil fertility. The results of this study highlighted the need for planning to improve wastewater treatment along with appropriate policies and methods to improve farmers' commitment for the environmental conservation and the human health.
