A whitish water ring often means moisture is trapped in the finish, while a dark stain can mean water reached the wood itself. Before treating it, identify the kind of mark and test any method in an inconspicuous area.
Separate white rings from dark stains
Pale rings are often within the finish and may improve as moisture leaves. Brown or black stains can penetrate more deeply and usually do not respond to the same surface treatments.
Start with gentle drying and patience
Remove any damp object and let the surface sit in a dry, ventilated room. For a recent white mark, time alone may release some trapped moisture without intense heat or aggressive products.
Avoid high heat, abrasives, and harsh home mixtures
A very hot iron, abrasive paste, or solvent can permanently damage varnish, lacquer, or thin veneer. If you try gentle warmth, keep it moving and at a distance, and stop if the sheen changes.
A dark stain may require refinishing
When discoloration is in the wood itself, removal may require sanding, wood bleach, or finish repair. On valuable or veneered furniture, a furniture restorer can prevent damage that is worse than the original stain.