トラブルシューティング6I got it wet and now I have water spots!
From "Leather in Japan No. 4" published in 2011
Use plenty of water to
Float stains and oil from the stain.
Leather products are basically not supposed to be wet with water. This is because when water dries, dirt and oil soaked into the leather precipitate at the border between the wet and dry areas, forming stains. Unlike surface stains, these stains cannot be removed simply by polishing the surface.
The best way to remove these water spots is to wet the entire leather with water and move the dirt and oil from its location. Therefore, the key is to soak the leather with plenty of water. If you wet only that area, the edges of the wetted area will become stained again, so it is essential to wet the entire area anyway.
Once the dirt that has been lifted by the wetting of the leather is removed, the leather can be restored to its original condition by drying it completely and giving it a moderate amount of oil again with a leather cream or the like.
A well-worn, slightly darkened bifold wallet. Rain drops from outside or water drops from a cup on the table have left stains on the surface.