Water quality improvement and operational performance of an ESP32-controlled rainwater harvesting system with gravel-sand-activated carbon filtration

Rooftop rainwater harvesting can reduce freshwater demand, but conventional systems often suffer from inadequate filtration, manual pumping, overflow losses and poor storage control. This study developed and evaluated an integrated system combining first-flush diversion, gravel-sand-activated carbon filtration and ESP32-based automatic sump-to-overhead-tank transfer. Across three rainfall events, filtration reduced turbidity from 19.4 ± 0.8 to 4.5 ± 0.3 NTU (76.8%) and total suspended solids from 62 ± 3.5 to 14 ± 1.2 mg/L (77.4%). The pH remained near neutral, and electrical conductivity decreased from 182 to 165 microS/cm. The automation unit achieved 97.5% average sensor accuracy, an approximately 2 s response time and 20 successful control cycles. Energy use was estimated as 97 Wh per 500 L transfer from rated pump power and calculated transfer time; it was not measured directly. Based only on the evaluated physical and basic chemical parameters, the system may support restricted non-potable applications such as toilet flushing, cleaning and gardening. Microbial disinfection and expanded chemical testing are required before wider reuse, personal-hygiene use or potable use.