An appliance using water including an incoming water valve is provided. The appliance also includes a sensor disposed in-line to an incoming flow of water received from the incoming water valve and is configured to sense a degree of hardness in the incoming flow of water. The sensor includes a substrate and a sensing element disposed on the substrate. The sensing element includes a sensing matrix, an indicator for one or more chemical species in a flow of water, and a selectivity component that reacts reversibly with the one or more chemical species in the water. The sensor also includes a light source configured to direct light through the substrate and the sensing matrix. The sensor further includes a light detector configured to receive transmitted light from the substrate and the sensing matrix and to generate a signal representative of selective wavelengths of the light indicative of the one or more chemical species in the flow of water. The appliance also includes a cleaning volume, a drain for the cleaning volume and an additive valve for an additive used for cleaning. The appliance further includes a controller configured to receive a signal indicative of hardness of the flow of water from the sensor and output it to control the incoming water valve, the additive valve and the drain on the cleaning volume.