Abstract: A highly versatile drive arrangement that drives a linearly reciprocating piston of a water conditioning unit control valve without imparting any significant side loads on the support structure for the piston's drive rod or the associated seals. The drive arrangement includes a reversible electric motor and a motion converter, such as a lead screw arrangement, that converts the rotary motion of the electric motor's pinion or other output element to reciprocating linear motion of the piston. The reversible motor can be controlled, based on signals from a motion monitor such as an encoder, to drive the piston to any desired position within the piston upon command. This, in turn, permits the operation of the water conditioning unit to be optimized for prevailing conditions and permits the control valve's operation to be altered if, e.g., the piston becomes stuck or encounters an obstruction.