water/fuel mixture detector

thank you for response of my previous title water/oil detector.but iam changing my title to that on the subject.my idea is to detect that there is water in a fuel(petrol or disel) stored in a tank.but iam restrict those whom are intrested to assist me in disign not include computeron that circuit.also remember the circuit should as simple as possible.i suggest the use of two paramiters ,that are condactance&ability of light to pass on these imiscible liquids.the system should be two inseparate ,one for water/petrol and the other for water/disel.nb.the system should be simlle to use any where