Abstract: A method includes receiving an ion concentration measurement from a sensor electrode measuring a fluid stream exiting a water conditioning system. A hardness metric is generated based on the ion concentration measurement. A regeneration signal is communicated to the water conditioning system based on the hardness metric. A system includes a sensor electrode to generate an ion concentration measurement in a fluid stream exiting a water conditioning system and a controller to generate a hardness metric based on the ion concentration measurement and communicate a regeneration signal to the water conditioning system based on the hardness metric.