Abstract: The present invention refers to a system and a method of filtering a refrigerant for a fluid injection system of an internal combustion engine, the refrigerant being preferably water, by supplying tap water or any other source of water available in the vehicle, such as air conditioning and exhaust condensates, wherein such water must be clean, demineralized, deionized and mainly promptly available to be delivered to the water injection system at the instant the driver actuates the accelerator pedal to demand more power from the bi-fuel engine running on gasoline.