Infrastructure systems are facing sustainability challenges but are locked into their current practices. Transitions studies aims to understand trajectories towards new socio-technical regimes and argue for agency-centric perspectives to explain processes of change. This paper adopts an institutional lens, examining the institutional creation processes needed for maturing innovations within established systems. Three innovations in Melbourne s water system were selected as empirical cases: desalination, wastewater recycling and stormwater harvesting. Each had a different institutional alignment with the established regime and different trajectories between key stages of maturity, from pre-niche to niche, niche-regime and regime. The paper examines the purposes and types of institutional work undertaken to support each stage: cultural-cognitive, normative and regulative. Their trajectories were influenced by the regime alignment and characterised by maturation speed, institutional work undertaken and limiting conditions for further maturation. Cross-case comparison enabled derivation of hypotheses on the linkage between institutional work and innovation maturity.