A respondent&#8217;s preference for non-market goods depends not only on the attributes of the goods but also on the respondent&#8217;s attitude towards the goods being valued. Accounting for these characteristics may substantially improve the ability of stated choice models to represent preference heterogeneity. In this regard, we analyzed the influence of respondent attitudes on the valuation of river ecosystem quality attributes affected by pulp mill wastewater in two central Chilean watersheds. We applied the Choice Experiment (CE) method to assess preferences on river pollution risk, water quality effects, threatened species and the yield in local fisheries. The payment vehicle was an additional annual charge to the electricity bill. All three environmental attributes and the payment attribute were highly significant determinants of choice (P<0.001). A calculated mean WTP value for an optimistic policy scenario was 13 USD/year per household. As hypothesized, attitudes influenced stated respondent preferences with some differences between the two studied watersheds. Overall, our findings suggest that attitudinal variables deserve more attention in the analysis of preferences for water resource improvements in emerging economies.