Abstract: The present invention relates to a method and device for measuring dielectrics in fluids, such as water. The sensor according to the invention comprises: a first printed circuit board (PCB) having a first side and a second side; a first and second conductor on a side of said first PCB; at least one galvanic connection between the first conductor and the second conductor; a first and second polymer affinity layer on a side of the first PCB; a second and third PCB, being equipped with holes and with a conductor plate; at least one galvanic connection between the first conductor plate and the second conductor plate; at least a first function generator; and a first spectrum analyzer or rectifier, wherein, in use, the sensor is placed in the fluid, and fluid contacts the polymer affinity layer through the holes and wherein impurities in the fluid are selectively absorbed and dispensed in the polymer layers thereby changing the dielectric properties of the polymer affinity layers.