Microbiologically Influenced Corrosion (MIC) refers to corrosion brought about by the presence and activities of microorganisms in biofilms, on the surface of pure metals or metal containing materials. Since the organisms involved, bacteria (aerobic and anaerobic), algae, fungi, and others, are generally ubiquitous, MIC can occur in almost every environment.  Each of these groups can cause different problems, not just corrosion. For example, slime forming bacteria can cause plugging, loss in efficiency of heat exchangers, clouding, taste and odor problems. Iron related bacteria, including iron oxidizing and reducing, can cause plugging, corrosion, cloudiness and color change.

If these nuisance microorganisms are present, MIC can occur on these surfaces as long as a nutrient source and water are also present. Their impact can make the water unsafe, unacceptable or unavailable due to losses in flow through plugging or equipment failure due to corrosion. Generally, testing for more than one group of bacteria with a combination of tests should be used to determine which ones are present and causing problems.