A new composite material based on alumina (Al2O3) modified by two surface nanocoatings – titanium dioxide (TiO2) and silver (Ag) – was studied for spa water disinfection. Regarding the most common microorganisms in bathing waters, two non-pathogenic bacteria Escherichia coli (Gram-negative) and Staphylococcus epidermidis (Gram positive) were selected as surrogates for bacterial contamination. The bactericidal properties of the Al2O3–TiO2–Ag material were demonstrated under various operating conditions encountered in spa water (temperature: 22–37 °C, presence of salt: CaCO3 or CaCl2, high oxygen content, etc.). Total removal of 108 CFU mL−1 of bacteria was obtained in less than 10 min with 16 g L−1 of material. Best results were observed for both conditions: a temperature of 37 °C and under aerobic condition; this latest favouring Reactive Oxygen Species (ROS) generation. The CaCO3 salt had no impact on the bactericidal activity of the composite material and CaCl2 considerably stabilized the silver desorption from the material surface thanks to the formation of AgCl precipitate. Preliminary tests of the Al2O3–TiO2–Ag bactericidal behaviour in a continuous water flow confirmed that 2 g L−1 of material eliminated more than 90% of a 2.0 × 108 CFU mL−1 bacterial mixture after one water treatment recycle and reached the disinfection standard recommended by EPA (coliform removal = 6 log) within 22 h.