The overall mechanism of an air compressor is a piston 
or rotary component (e.g. rotary screw or vane) that allures surroundings, which is compressed into a storage tank. Naturally, Water Lubricated Air Compressor because the piston or rotary component needs to move regularly and smoothly for this to function, it generally needs to be lubricated.
In a lubricated air compressor, there is lubricating oil which will keep the piston or rotary element running well without damaging the system. The lubricant also helps to dissipate high temperature and maintain air compression efficiency.
Oil-totally free air compressors also use a piston or rotary element, but they get around the lubrication problem by coating the compression element with a pre-lubricating material like Teflon. Some oil-free compressors may also use water in place of essential oil for the lubricating and cooling process. These alternate materials defend the pump and allow the mechanism to move smoothly without the need for any oil-based or synthetic lubrication.