Water is subject to heterogeneous uses that put pressure on it and create rivalries between competing users. This article analyses the conditions under which challengers are successful in gaining access to the resource and in imposing a change of behaviour on the incumbent users. It asks whether the acquisition of property rights is the only means for a challenger to get access to the resource. The empirical study compares 11 ‘most different' cases of water rivalries in four water basins. It shows that two main ‘paths' explain success: Either the challenger activates a property right and negotiates a solution at no cost for the incumbents, or he activates a public policy that grants him a credible alternative to a negotiated agreement. Thus, the challenger must select the kind of rule, property right or public policy, that supports his position and, then, elaborate an appropriate strategy to impose this rule.