Interestingly, we used to use tap water daily on a previous model of the same engine series, with the full knowledge of the contracted maintenance organisation which is also an accredited agent of the engine supplier. For 8 years we never had a contamination problem despite operating low level close to the sea.
When we replaced the old aircraft with one powered by a later model of the same engine we asked if we could continue that practice and were told we couldn't; not because of the water but because it's technically more complex so chemical washes every 50 hours would be acceptable. In hindsight it would seem that this was actually because they hadn't anticipated needing to supply the wash kits in that quantity.
Now that the UK fleet is showing signs of contamination the manufacturer has decided a daily wash with distilled or deionized water is the only way.
I can quite see the point about mineral content of domestic water, but what is annoying me at the moment is 1] if tap water was OK for so long why is it suddenly not, and 2] it can't be beyond the wit of a major engine manufacturer to specify a minimum water quality, and if our local supply is better than that surely we don't have a problem.
I washed many an engine on offshore operations and I have to admit I never asked what was in the rinse tank; what do the North Sea and other operators use?
How spooky is this - literally minutes after I posted this lot an email arrives to state that the manufacturer is looking again at the question of local water analysis.
