First and foremost, dirty fuel can cause damage to your fuel system and engine components simply by passing through the system. Microscopic particles of dirt and grime can clog fuel filters and injectors, reducing engine efficiency and ruining the injector spray pattern. Water is vaporised as it passes through the injectors, causing damage to the injector tips, which also ruins the injector spray pattern. In addition, water in your fuel creates the perfect environment for fungi to grow, feed, and defecate throughout your fuel system.
These abrasive contaminants then pass through the system, causing additional, unnecessary wear and tear on the components, which in turn reduces their lifespan and costs you more for repairs and replacements.