It does matter if your item is aniline or non-aniline dye , as far as cleaning goes .
You might want to check out some research on this , prior to trying to remove the stain .
Cleaning , of course , will tend to remove patina .
If you're sure it's a water stain , use a new (& very well rinsed , since most manufacturers use a sanitizing agent on them) sponge .
I rinse out the sponge with tap water , then use several rinsings with distilled water .
Wring out your sponge until it's as dry as you can get it , then gently wipe (don't scrub) outward from the center of the water stain .
Try not to 'soak-down' the leather with water .
Allow your item to air-dry (not using heat) and consider using something like 'Tannery Vintage Leather Cleaner & Conditioner' on your leather , since almost any amount of water on leather causes some 'drying out' .
I've used this method , per the advise of my Art Conservator , with really good success (never on any suede leather , though) .
Old-timers used to remove water stains with a solution of vinegar & linseed oil .
Cool plaque , Dean .
