Aqua-Rex treats all the water in the home, all the time. It sends a signal into the water heater even when no water is flowing and it also sends a signal back into the cold supply in the rest of the home so mixing valves, showerheads and kitchen faucets won’t get scaled up either. It is OK to treat the water to the kitchen faucet because it doesn’t add unhealthy sodium to the water, instead it retains the healthy calcium.