Message: I have a silk dry clean only dress that has a water stain on it.  Dry cleaners cannot get stain out so I want to dye it.  Is it possible?

Dyeing is impossible without a great deal of washing. You have to prewash to remove invisible stains that will interfere with dye absorption, and you need to wash repeatedly after dyeing to remove any loose unattached excess dye.

What you need to do now is wash your dress in water to try to remove the water spot. If this works, you won't need to dye it; if it doesn't work, there's no point in dyeing it. Silk is often washable. If yours turns out not to have been washable, you'll have to discard it, but since that's essentially the situation you're in right now, you may as well try.

If a dress is unlined, chances are that it will survive washing, though you might find that the original manufacturer did not bother to use high-quality wash-resistant dyes. It's possible that the original dyes will dissolve in the water. You may find that this takes care of the water spot, with no need for further action.

If the dress is lined, I predict that problems in fit will arise from washing. The lining is typically made of a synthetic fiber (often not mentioned on the content label), which will not shrink as much as the natural fiber; when the lining is a different size from the outside layer, the garment is ruined. 

Since your dress is currently unwearable, though, it's probably worth the risk of washing it. Don't even consider dyeing until after you have successfully washed the dress.

Followup:

Thanks so much for the advice.  We washed the dress and the water stain came out - no need to dye.  Maybe a small amount of shrinkage but still very much wearable.
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