A fuel system comprising a liquid fuel tank, an engine, and a cyclonic separator having an inlet fluidically connected to the fuel tank, a first outlet fluidically connected to an engine fuel feed system, and a second outlet. The cyclonic separator is adapted to discharge relatively denser material from the first outlet and relatively less dense material from the second outlet. The fuel system may be used to remove water or ice from the fuel tank by separating the liquid fuel in the tank into water rich fuel and purified fuel using the cyclonic separator. The water rich fuel is discharged to the engine where the water is burnt off with the fuel. The cyclonic separator may be retrofit in an existing fuel system. The fuel system may be in an aircraft.