A device for use in determining the depth of water accumulating on the surface of a pathway, such as an airport runway or the like. A block of electrically insulative material is embedded in a pathway with the top surface of the block being substantially flush with the pathway surface and exposed to atmospheric precipitation. A sensor comprising first and second capacitors, each of which has first and second coplanar spaced apart electrodes, is positioned within the block with the electrodes of the first capacitor positioned adjacent to and inclined with respect to the top surface of the block and with the electrodes of the second capacitor being positioned a substantially greater distance from the top surface of the block whereby an accumulation of water on the surface of the block affects the dielectric, capacitance and conductance of the first capacitor without substantially affecting the dielectric, capacitance and conductance of the second. Time-varying out-of-phase electrical signals are applied to the first electrodes of the capacitors as the input to the sensor. An output circuit commonly connected to the second electrodes of the aforesaid capacitors supplies an electrical output signal relative to electrical ground from the sensor. At least one electrical conductor within the block is connected to electrical ground with a portion thereof exposed to the atmosphere at the top surface of the block. Accumulation of water on the surface of the block affects the capacitance and conductance between the output circuit and electrical ground whereby the amplitude of the electrical output signal of the sensor is a function of the depth of water accumulating on the surface of the pathway.
