Methods of compressor performance maintenance for large utility combustion turbines continue to evolve. On-line water wash systems used to recover performance loss due to fouling are evolving that use less water. This paper derives a water wash model based on a thin film of water covering the airfoil surfaces. The economic potential for recovering “unrecoverable” losses due to increased roughness and erosion is evaluated. As an outage is needed to remove the compressor cover and perform the maintenance, the approach is to identify the most beneficial maintenance actions and an optimal maintenance interval.