This study aims at investigating how economic inequality affects the possibilities for successful water cooperation between neighboring states sharing a transboundary watershed. As of 2019, researchers have concluded that there are 310 international river basins affecting 150 countries and 52 percent of the world’s population. Drawing on theories from research on cross-border cooperation and openness focusing on the relative attributes of bordering states, the hypothesis is that the more economically equal two bordering states are, the more they will cooperate regarding their shared waters, while the total economic development of the dyad will also have a positive effect on transboundary water cooperation. Initial regression analyses show no effect of economic inequality in a dyad on its transboundary water cooperation, while the effect of the accumulated economic development is significant. However, after including control variables on joint democracy, cultural similarities, conflict history, quality of government and region in the model, economic inequality is shown to have a statistically significant effect on transboundary water cooperation. Contrary to the predictions, this correlation is positive, which means that economic inequality between riparian states actually enhances cooperation in this study. One possible explanation may be the power imbalance economic inequality creates, which might allow the economically more powerful state to dictate the terms and impose cooperative arrangements on the weaker state that serve its own interests.