The ASTM D 2247-15 (2020) standard provides a method for testing coating water resistance at 100% relative humidity. This method evaluates the coating's water resistance by placing the coating sample in an environment with 100% Humidity so that condensed water droplets form on the surface of the sample. The testing process involves placing the sample in a sealing chamber filled with heating water vapor and observing the change of the coating by controlling the time and Humidity. The key to the testing is to evaluate the color change, blistering, adhesion drop, etc. effects of the coating under this extreme Humidity condition. This test method is important for durability and quality control of coatings, but results may differ from actual performance in the natural environment.