Remove Water Stains From the Ceiling
You have fixed a leak or other cause of water damage, but the water stain is still there. However, you may not need to repaint or repair the ceiling. Try spraying bleach into place.
A family handyman recommends spraying the stain with an aqueous solution of bleach (10 percent bleach). After a day or two, the stain may disappear. However, if it is an old stain, they recommend using a mold and mildew remover. Protect the walls and floor – and, of course, your eyes.
10 Minute Home Renovation and Maintenance Tips | Family Handyman