Abstract: A device adapted to be placed between a fuel storage tank and a fuel container into which the fuel is to be pumped, for example on a fuel pump nozzle, for detecting the presence of water in the fuel being pumped. The device has a tubular member with an inlet for receiving a portion of the fuel being pumped, an outlet for discharging the portion of fuel conducted through the tubular member, and a transparent portion disposed between the inlet and outlet. A chemical paste composition containing a water responsive indicator dye is disposed in the transparent portion of the tubular member to contact the portion of fuel conducted through the tubular member and produces a visually noticeable color change indicating the presence of water in the fuel being pumped.