The compressor of a gas turbine ingests a large amount of air. This air contains particulate matter, aerosols of hydrocarbons and other organic compounds and gases of industrial production such as nitrogen, chlorine and sulphur. Although the larger particulate matter is filtered out, the other compounds and the fine particulate matter are deposited on the compressor blades. This alters the aerodynamic profile of the blades and leads to a fall in compressor efficiency. Compressor washing removes this deposited fouling, restoring the aerodynamic profile and compressor efficiency.