For vulnerable groups in society, water insecurity and deficient water availability for food production commonly reflect unequal distribution of water volumes, quality, and services within unequal power structures. Water security is necessarily a political dilemma. Policy debates, however, tend to naturalize and de-politicize this concept. Instead of recognizing that water security and distribution belong to the realm of human interests, choices, negotiation, and power plays, they are often represented as following universal economic, legal, and natural-scientific rules. In this context, there is a widespread policy assumption that formally recognizing local, customary water rights is one important element to grant water security for marginalized user groups. This paper challenges this assumption and examines the illustrative case of a Peruvian Andes community, Yanque. We scrutinize formalization policies that claim to enhance water security for marginalized communities regarding (1) material water allocation and (re)distribution and (2) water rulemaking, legitimate authority, and cultural-political organization—both elements that stand central in formalization processes. We discuss the complex relationship between formal and alternative “water securities” and the cultural politics of rights recognition and show that uncritical formalization of local water rights often leads to weakening rather than strengthening local water security.