Once in the system, water can be removed by using water separating filters or devices. Long term prevention of problems associated with water in fuel is best accomplished by obtaining fuel from reputable suppliers capable of providing high quality fuel. Further, fuel tanks should be kept well filled to prevent condensation, and fuel should be drawn from the top of a tank if possible, as water is heavier than diesel fuel and tends to settle to the bottom of tanks. Wax crystals form as a result of cold temperature precipitation of paraffin. Temperatures below a fuel's cloud point will result in wax precipitation and filter plugging.
Fuel suppliers blend diesel fuel based on local anticipated cold weather conditions.
For example, fuel purchased in the West or South may not be suitable for operating conditions in the Midwest or North. Called Humbugs for short, these active and multiplying colonies will spread through a fuel system and quickly plug a fuel filter. The fuel filter will have a slime coating over the entire surface of the media. Bacteria may be any color, but is usually black, green, or brown. Draining the fuel system will reduce microbial activity, but it will not eliminate it.