Most internal combustion engines use a fuel filter, in order to protect the components in the fuel system.
Unfiltered fuel may contain several kinds of contamination, for example paint chips and dirt that has entered the fuel tank while filling, or rust caused by moisture in a steel tank.
[citation needed] If these substances are not removed before the fuel enters the system, they will cause rapid wear and failure of the fuel pump and injectors.
Some diesel engines use a bowl-like design to collect water in the bottom of the filter (as diesel floats on top of water).
[citation needed] The water can then be drained off by opening a valve in the bottom of the bowl and letting it run out, until only the fuel remains.