An increasing scarcity of water for crop farming and livestock watering among agropastoralists of Mieso in Eastern Ethiopia has largely disrupted their livelihoods. Indigenous water well maintenance and government initiated rainwater harvesting are two important collective actions common among these communities. With the aim of examining collective action institutions in both cases, we collected data from different stakeholders and individual members. Theoretically, low level of physical assets (action resource) limits participation of an individual in collective action. In our case, other factors such as environmental uncertainty and lower level of dependence on the resource have been found to be more significant in limiting membership than limitation of assets. Poor agropastoralists depend on their informal networks to have access to other assets. This enables them to maintain their membership. Moreover, there is a difference between self-organized and imposed collective action in terms of rule enforcement and sanctioning. Institutions also produce different incentives in that free riding leads to automatic exclusion in water harvesting, whereas poor free riding members continue benefiting from the water well. In evaluating the success, we conclude that technical capacity of members in benefiting from their collective action is limited and deserves more attention than their ability to develop effective collective action institutions. Technical capacity development of user groups needs to be central in policy and programs addressing this.