That is called a compressor wash and should be done to all turbine engines after a flight in a salt laden environment, ie any cloud around the UK! To those of a certain age distilled water was used, to those yong'ns it is ionised water.
In the early eighties, 72 Sqn used to clean the Gnome compressors on their Wessex helicopters using a process called a Turco Blast. Basically an abrasive substance called Turco was fed through the engines during a dry run to clean the compressor blades by removing any deposits. Turco was made up of ground apricot seeds. I cannot recall exactly when these were carried out but I seem to recall after flying in a salt water environment.