During transport and storage, fuel is often decanted many times from tank to tank, and whether through condensation or leakage, moisture is able to infiltrate the fuel.  Fungal spores, yeast, and bacteria are commonly found in almost any environment and a fuel tank provides the perfect breeding ground for the growth and spread of these contaminants.  The most common of these is “Cladisporium Resinae” - the Diesel Bug.  At its worst, serious infestations can cause complete breakdowns, however even mild levels of contaminants can quickly lead to fuel degradation and costly maintenance.  The presence of water also increases the susceptibility of fuel tanks to rust and corrosion, leading to deposit formation and further fuel degradation.