A water conditioner that utilizes ionic flow and selective ionic filtering to control water hardness and/or pH. In some embodiments, the water conditioner includes one or more conditioning cells each having electrodes and a cathode side and an anode side separated by an ion-selective filter. The ion-selective filter is design/configured/selected to pass alkaline earth metal cations and block corresponding carbonate anions. When the electrodes are energized and water is present on the cathode and anode sides of the filter membrane, the alkaline earth metal cations pass from the anode side to the cathode side through the membrane, while the membrane blocks carbonate ions on the cathode side from passing to the anode side. In this manner, alkaline earth metal cations, and water hardness, can be reduced in the anode flow.