GB/T 30648.2-2015 "Paints and varnishes - Determination of resistance to liquids - Part 2: Water immersion method" specifies a test method for evaluating the water resistance of single or composite coatings partially or fully immersed in water, used to assess the impact of water on the coating surface and substrate. The test apparatus includes a water tank made of inert materials, a non-conductive specimen holder, a water circulation system, and a temperature control device with an accuracy of ±1°C. The test water must comply with the Grade 3 water standard or seawater may be used. Specimens are placed on the holder at an angle of 15-20° (with a spacing of not less than 30 mm) and immersed in water at a temperature of (40 ± 1)°C. Water resistance is determined by observing changes in the coating, providing a basis for evaluating the quality of related products.