Non-washable painted walls are usually paint with flat paint or the dreaded "builder paint" in new homes, which will often wash right off the wall with even a mild cleaning. Low quality satin or semigloss paint may also be permanently streaked by cleaning attempts. While there's no way to clean deep stains and heavy grime from non-washable painted walls without ruining the surface, there are ways to minimize the damage; and if you're careful, you should be able to clean small scuffs and marks without leaving any evidence.
Dust or vacuum the wall first, even if it doesn't look dusty. Cleaning will rub even invisible dust into the porous painted surface, leaving a dirty-looking mark.
Rub scuff marks and small blemishes gently with a dry dirt eraser sponge designed to remove stains and marks from painted surfaces without the use of water.
Mix a mild cleansing solution in a clean bucket, such as one part white vinegar to three parts cool water, or 2 tbsp. Borax to a gallon of water. Fill another bucket with clean cool water for rinsing.
Clean the wall using the cleaning solution and a clean rag or sponge. Start at the bottom and work up to the ceiling working in approximately 3-foot wide sections. Use very light pressure while cleaning.
Squeeze excess water from the rag in your rinsing bucket and rinse each section as you go, working from the ceiling to the bottom of the wall.