Improving irrigation systems in Asian countries has been a high priority for the allocation of international aid. Substantial funds have been allocated to adopt the “best practices” of hiring external water engineers to construct modern systems to replace those that farmers built. These expensive investments have infrequently led to long-term improvement in the operation of irrigation systems in Asia. In this article, we examine the process and impact of an innovative irrigation assistance project that was initially undertaken in Nepal in the mid-1980s. We analyze data obtained over three time periods related to changes in system structure and performance over time. We trace the unfolding patterns of improved engineering infrastructure across time depending on the way it interacts with other factors to affect long-term irrigation performance. We examine some of the key variables that are likely to affect the diverse and complex patterns of change. We also undertake analysis of the configural impact of core variables using Qualitative Comparative Analysis (QCA). We find that the initial and later investments in system infrastructure are only one factor that helps to generate short-term improvement. Unless farmers encourage local entrepreneurs and organize themselves, create their own rules or use sanctions, and augment their rules through collective action, infrastructure investment alone is not sufficient to achieve sustainable higher performance.