Drinking water treatment residuals (DWTRs) provide an opportunity to further embrace circular economy in the urban water cycle. DWTRs surface properties can be improved by chemical functionalization to enhance the pollutant removal performance. Fe/Al-DWTRs were functionalized with nanostructured calcium silicate (nanoCSH) to remove Cu(II) and As(V) from rivers, simulating an accidental acid spill. Model raw DWTRs were generated using raw water. DWTRs were physicochemically characterized by a multi-technique approach (SEM-EDS, FT-IR, BET, XRD). Sorption experiments were performed using Cu(II) and As(V) by varying the initial pH and DWTRs doses. Compared with raw DWTRs, NanoCSH_DWTRs demonstrated a higher removal efficiency in acidic settings, faster removal rates, and higher effectiveness at lower dosages. Kinetic and equilibrium sorption experiments were performed. Experiments simulating accidental Cu and As pollution from acid drainage revealed that NanoCSH_DWTRs had a higher collective removal of As(V) when Cu(II) was present, most likely due to the synergistic relationship formed by the tertiary metal-surface complexes. An application approach was implemented using theoretical case studies. NanoCSH_DWTRs reduced the dose required to treat metal(loid)-enriched water compared to raw DWTRs. NanoCSH_DWTRs would provide an alternative as a first line of de-fense against the accidental release of acidic drainage.