This paper focuses on the often-overlooked issue of soluble salt contamination testing and removal during surface preparation prior to coating application. Soluble salts, including chlorides, sulfates, and nitrates, left on the surface prior to coating application can lead to osmotic blistering, corrosion, and coating failures. Several standards provide methods to test for soluble salts. However, there is no industry consensus on acceptable contamination levels given the diversity of coating systems and environments. This paper serves as a guide intended to shed light on the specific issue of soluble salt contamination, particularly on carbon steel surfaces. By addressing the nuances and challenges posed by soluble salt contaminants, this paper aims to equip engineers and professionals in the field with the knowledge and tools necessary to navigate the complexities of surface preparation and ensure the integrity and longevity of coating systems on carbon steel surfaces.