Flow sensors for measuring the flow of an ion-containing fluid may be implemented using mechanical or electrical techniques. Mechanical flow sensors are have moving parts and therefore may be unreliable after some time and are expensive to manufacture. Hall-effect type flow sensors typically require a reversible magnetic field to compensate for electrochemical effects. A flow meter including such a sensor uses an electromagnet. A flow sensor (100) is described using a capacitive sensor (10) and processor (12) to determine the flow rate from a change in capacitance and a magnetic field. Such a flow sensor may be implemented using CMOS technology. The flow sensor may operate in a magnetic field generated by a permanent magnet and measure the flow reliably.