This dataset supports the PhD research project “Assessing the hydrologic benefits of water sensitive urban design in tropical cities: evidence from low-cost sensor monitoring.” The dataset includes laboratory performance assessment data for low-cost water level sensors; field monitoring data collected using an IoT-based low-cost sensor monitoring system deployed at a rain garden in Singapore and a green roof in Bangkok, Thailand; and Personal Computer Storm Water Management Model (PCSWMM) project files used for hydrological modelling. All associated Arduino and R scripts required for data acquisition, processing, and analysis are provided.