An optical water-quality detection apparatus includes a detection device, a biofilm-inhibition light source, a detection light source and a sensor. The detection device includes a detection chamber. The biofilm-inhibition light source is disposed outside the detection chamber and configured to emit biofilm-inhibition light. The detection light source is disposed outside the detection chamber and configured to emit detection light. The sensor is configured to sense the detection light penetrating the detection chamber. A beam of the detection light and a beam of the inhibition light overlaps as penetrating the detection chamber.