For testing for the presence of water at the bottom of fuel storage tanks. Suitable only for use with Petrol, Diesel, Kerosene, Gas Oil, Heating Oil, Heavy Oil, and Lubricating Oil. Applied to a rod or length of string with a bottom weight, the brown paste changes colour to brilliant red where it comes into contact with water, giving a visual indication as to the depth of the water present. The water can then be pumped out, and the test repeated until there is insufficient water to pump. No official expiry date, will keep best when stored between 31F and 115F.