Transnational public-private partnerships (PPPs) are new forms of governance that have caught the interest of researchers in recent years. While the literature tends to portray PPPs as loosely institutionalized forms of governance, we argue that PPPs' institutional design varies and matters for their effectiveness. We aim to demonstrate that a high degree of institutionalization (obligation, precision, delegation) is relevant in cases that involve collective action problems—that is, for those PPPs that have to deal with distributional conflict, cheating, or free-riding. To substantiate our argument, we compare and analyze the performance of three transnational water partnerships (not to be confused with municipal for-profit PPPs). Our results confirm that a high degree of institutionalization tends to be important for those water partnerships that implement costly projects. It is less important for those that focus on the comparatively undemanding task of exchanging and disseminating knowledge and best practice in water management and governance.