A water lubrication screw type air compressor includes a compressor, an air-loop system and a water-loop system. The water-loop system includes a water supply device, a first water-loop unit and a second water-loop unit. The water supply device includes a first water-treatment device to modify the water quality and provide purified water. The first water-loop unit includes a second water-treatment device to modify water quality and reduce the corrosion of metal components. The second water-loop unit includes a water filter to remove the impurities in water and maintain the purity of cycling water. Therefore, the water-loop system in the present disclosure includes multiple water-treatment devices and filters to maintain the water quality. The purified water ensures better cooling, lubrication and air proofing when injected into the compressor.