Color kut water finding paste is used to test for the presence of water in the bottom of oil, diesel, petrol, gasoline, fuel oil and kerosene tanks. The brown paste is applied to a weighted string or rod and dipped to the bottom of the tank. The section of the paste that touches water will immediately turn a brilliant red upon contact. Then, Once the rod is removed, you can determine the depth of the water by the paste that has changed color.