MONITORING AND EVALUATION OF THE QUALITY OF RAINWATER HARVESTED FROM ROOFTOPS FOR REUSE AND SUSTAINABLE APPLICATION IN MACAO

Macao, a densely urbanized region with limited freshwater resources, faces significant challenges in water security, relying on over 90% of raw water imports from the Mainland. This study investigates the quality of rainwater harvested from three representative rooftop types (blue metal, concrete, and green garden roofs) to establish a scientific basis for sustainable reuse. The research reveals distinct water quality patterns and first-flush effects across roof materials through field sampling and laboratory standard of parameters, including organic matter, turbidity, and nutrients.
Key findings show that green roofs exhibit the highest pollutant concentrations (e.g., COD: 52.27 ± 26.00 mg/L and conductivity: 525.75 ± 203.60 μS/cm) due to vegetation decomposition and soil leaching. In contrast, blue steel tile roofs yield relatively cleaner runoff but with pronounced initial pollutant surges. Concrete roofs produce alkaline runoff (pH up to 8.63) due to cement mineral dissolution. Statistical analysis confirms conductivity and turbidity as robust predictors of dissolved pollutants, with significant correlations to other parameters, enabling rapid water quality assessment.
The study further evaluates the first flush effect; recommendations include material-specific collection strategies, IoT-integrated smart monitoring systems, and policy incentives for green roof adoption to balance ecological benefits with water quality management. This research addresses critical gaps in Macao's rainwater management, providing a sustainable urban water resource optimization framework.