Urban catchments increasingly face water-related challenges driven by rapid development and climate change, while conventional stormwater management is often insufficient for removing gross pollutants and sediments. This study evaluates an integrated treatment approach combining continuous deflective separation (CDS) technology with nature-based solutions (NbS)—including biochar, green zeolite, and floating wetlands planted with Vetiver grass—implemented at a commercial urban site in Malaysia. An on-site Internet of Things (IoT)-based monitoring system tracked pH, turbidity, electrical conductivity (EC), dissolved oxygen (DO), total dissolved solids (TDS), and temperature. Additional parameters, including biological oxygen demand (BOD), chemical oxygen demand (COD), nitrate (NO3−), total suspended solids (TSS), heavy metals (Pb, Cu, Zn), and nutrients (N, P), were analysed at the accredited laboratory of the National Water Research Institute of Malaysia (NAHRIM). Results indicate that biochar and green zeolite enhance system performance by adsorbing micro- and near-nano-sized particles and nutrients, preventing clogging, and achieving removal efficiencies of 57% for TDS, 90% for TSS, 78% for NO3−, 50% for oil and grease, 80% for BOD, and 57% for COD. Floating wetlands further improved removal of ammoniacal nitrogen (NH3-N) and phosphate (PO4³−), key eutrophication contributors. The study also demonstrates circularity: harvested Vetiver is processed into economic products, while residual biomass is converted into new biochar via pyrolysis to replace saturated biochar, which is then reused as compost. The integrated CDS-NbS system improves stormwater quality, supports reuse, contributes to carbon sequestration, and aligns with the United Nations sustainable development goals (SDGs).