Gas Turbine compressor efficiency and long term operability are highly affected by the air quality entering the compressor through its intake air filtration system. This case study presented the experience of an industrial Gas Turbine application in Singapore that has had a retrofitting project to improve the filtration system performance. The retrofitting scope comprised mainly of an upgrade to filter efficiency class and the intake system design to minimize fouling agent and rainwater ingression into the compressor. The two-pronged approach resulted in slower deterioration of compressor efficiency as well as reduction of offline water wash frequency. While the results benefited the compressor performance, the filters run length was found to be too short than expected.