The present invention relates to a vehicle system (80) configured for injecting an aqueous solution in an air intake line (12) upstream of a combustion chamber (14) of an internal combustion engine, or in the combustion chamber (14) of the internal combustion engine, said vehicle system (80) comprising the following constituents: ⋅a tank (16) to store an aqueous solution; ⋅a pump (18); ⋅an air intake line (12) upstream of a combustion chamber (14) of an internal combustion engine; ⋅one or more injectors (20) configured for injecting aqueous solution in the air intake line (12), in the combustion chamber (14) or both; ⋅a feed line (22) configured in for feeding said injector (20) with aqueous solution pumped by the pump (18). In the vehicle system, at least a portion of at least one of the vehicle system constituents (16, 18, 12, 20, 22) or of a tank (16) component (24) is made of a polymer material. The polymer material—comprises an effective amount of at least one antimicrobial agent, or—has on its surface a surface coating containing at least one antimicrobial agent, the surface coating comprising between 0.001% by weight and 0.25% by weight of the at least one antimicrobial agent.