• We tested a low-cost water level sensor compared to a traditional sensor in the laboratory, and the results showed a great potential for the low-cost sensor to be used in field monitoring practices. • Three months field observations showed that the low-cost sensor functioned as expected and was able to effectively monitor the water level variation for the WSUD system monitored. • The performance of the WSUD system in terms of stormwater retention will be evaluated based on PCSWMM model that will be calibrated with the empirical data collected from the low-cost sensor monitoring system.