The present invention relates an optical sensor. In particular, the present invention relates to an optical sensor for detecting chemical components in a fluid.The present invention comprises two or more sensors, each being configured to detect one or more chemicals in a fluid, or one or more properties of the fluid, and two or more light sources. Each sensor is associated with one light source, and each sensor is configured to emit or reflect light in response to light from the light source incident on the sensor. The emitted or reflected light is dependent upon the presence of a chemical or a property of the fluid. The two or more light sources and two or more sensors are arranged around a single light detector, which detects the color and/or intensity of the light being emitted or reflected by the sensor. Data from the light detector is passed to a remote processor for processing.