In this paper we compare recent efforts towards the constitutionalization of the right to water in Brazil, Colombia, and Peru to understand the opportunities and limitations related to the attempts to enhance access to piped water to the highest normative level. Peru passed a constitutional amendment in 2017 while Brazil and Colombia have seen much right-to-water activism but have not succeeded in passing such reforms. We explore the role of the existing domestic legal frameworks on drinkable water provision and water management towards the approval of constitutional amendments. We find that all three countries have specialized laws, water governing institutions, and constitutional jurisprudence connecting access to water with rights, but the legal opportunity structures to enforce socio-economic rights vary; they are stronger in Colombia and Brazil, and weaker in Peru. We argue that legal opportunity structures build legal environments that influence constitutional reform success. Legal opportunity structures act as incentives both for social movements to push for reforms and for actors with legislative power to accept or reject them. Our findings also show that in some contexts political cost is a key element of constitutional reforms that enshrine the right to water; therefore, this is an element that should be considered when analyzing these processes.