Create a cleaning mixture to remove the water stains and marks from the painted ceilings and walls. Fill a large bucket with 1 gallon of warm water. Mix 1 cup white distilled vinegar, 1 cup baking soda, and ½ cup ammonia into the warm water.
Clean the painted walls and ceiling with the mixture and a sponge or damp towel. This initial cleaning should help you determine whether the water stain is going to be removed. Once the wall is clean, wipe it down with a dry towel.
Cover tough water marks in the paint with shellac and a paintbrush. You cannot simply paint over the marks with latex paint because the stain will seep through the paint. Instead, cover the mark with shellac and let dry per manufacturer directions.
Touch up the latex paint with leftover or matched paint and a paintbrush. Let the paint dry per manufacturer directions.