Rainwater harvesting (RWH) is increasingly adopted as a decentralized water source, yet there are no regulations or policies ensuring its safety for drinking purposes. This paper introduces a five-step iterative framework to build a water quality monitoring plan for such systems comprising system description, monitoring parameters, monitoring frequency and timing, monitoring techniques, and data storage and analysis. To illustrate its practical application, the framework is applied to Superlocal, a community scale rainwater harvesting project in Kerkrade, the Netherlands, where rainwater is collected and treated locally to supply drinking water. Applying this framework, the manuscript provides detailed implementation guidance. In the absence of specific RWH regulations, the study adapts existing Dutch drinking water regulations (DWB and DWR) and utilizes a historical rainwater quality database to inform parameter selection, thresholds, and monitoring frequencies. The analysis reveals that water production and monitoring costs for Superlocal total €4.60/m3, considerably higher than for centralized systems in the Netherlands. As decentralized RWH systems are increasingly integrated into climate adaptation strategies for urban water, this work highlights barriers and enablers for advancing safe and sustainable decentralized water management. The study recommends policy interventions and cooperative management models to enhance the economic viability and safety of these systems.