Hmmmmmm.....yet to see any proof that washing kites in fresh water is detrimental. I used to wash mine regulary with tap water and it did keep them in noticeably better condition than friends who did not. It removes sand and I have also read that it reduces the effect of salt crystals that can be abrasive and focus the suns rays but I've yet to see proof if this. UK kiter experimented trying to get mildew to grow on kite material in a variety of conditions and failed.
From my experience washing kites regulary with fresh water and occasional cleans with mild detergent keeps the fabric in better condition.
Major kite killer is leaving them flapping in the wind!!! Breaks down the fabric.
You might be right ?
Because, if you rinse your kites like that, you are by nature most likely more caring about your gear, than most of your friends - thus your gear WILL of course be in better condition than theirs, over the years - but not necessarily because of the tap water rinsing
As said, you can also be right - but the argument itself that yours hold up better is not valid IMO.
Regarding Mildew Noel - it does not always take 3 days to occur !
It can happen overnight - just one night left with fresh water, and your kite can look ugly as hell, with NO way to get rid of it whatsoever
On the other hand, one can be lucky, that even with freshwater rinsing or rain - the kite can be stored wet for endless amount of time without getting "brown" (mildew) on the white areas especially.
So the very nature of mildew is very complex, and you can not know if it will happen or not.
I never ever waste time on rinsing, but if rain-wet I try to dry as good as possible to avoid a shitty looking kite, literally taken.