Great question!! The first step to get rid of your unsightly water spot is to diagnose and repair the cause of the leak. Like most things in life, you can’t just cover up the surface without fixing the root problem. The leak may not be directly above the spot. It could be a roof leak, leaking plumbing pipe or condensation on anything made of metal above the ceiling. Consider having a qualified contractor diagnose and repair the leak. The resulting water spots are very obvious and unsightly, but are actually fairly easy to fix. We would be glad to come out and take care of it for you but you can do it on your own with limited cost.
Necessary Supplies
You will need a stain blocking primer such as a simple spot primer in a spray can or you can paint it on with brush and roller. Our go-to product for blocking stains is Sherwin Williams Pro Block oil based primer. Another good product to use is Zinsser’s B-I-N stain blocker. You will also need flat white ceiling paint, step ladder, drop cloths, extension pole, safety glasses, paint roller and cover, paint brush, paint tray and liner, painters tape (unless you have a very steady hand) and great music to keep your motivated.
The Process
The Prep:
The worst part of the process is having to worry about all the things you could mess up while painting. Take down all fixtures or cover them well. Remove as much furniture as possible so you can maneuver as easy as possible throughout the room. Use drop cloths to protect any remaining furniture and carpets from paint splatter. Make sure the room is well ventilated before using primer.
The Primer:
Because water spots are made of well……water, it is always best to prime them with an OIL based primer. A water based primer will allow the dark stain to bleed through. It may cover the stain initially, but after a week or so…..peek-a-boo! This is also why you can’t just cover water stains with a coat of paint. Water and water don’t mix. We know it’s stinky, but go ahead and bite the bullet to insure you never see that stain again. This would be a good time to mention another favorite product, the Odorless Oil Based Stain Blocking Primer by KILZ. Apply a coat of primer over the area and slightly beyond with a roller, brush, or for small stains spray an even amount of aerosol blocking primer. 
Some people are satisfied after this step and stop. If the ceiling has nicotine discoloration, grease spots, or soot it is best to apply the stain blocking primer to the entire ceiling before applying a coat of the ceiling paint.
The Paint:
In most cases it has been a while since you last painted your ceilings, and you will find that the new, fresh white ceiling paint is considerably brighter than what you thought was a white ceiling before. It is almost always recommended to paint the entire ceiling for color uniformity. In some cases you might be able to blend the paint around the small water stain to match the rest of the ceiling. Usually a brush is best for this to “feather in” the new coating with the old. A roller leaves a pretty harsh stop line for the amateur painter.
There ya have it! Easy peasy, right!? Those water spots are now gone. You’ll likely never find anyone who really enjoys painting ceilings but the end result is worth the effort. You won’t need to repeat the process for a few years. How many years? Most people choose to repaint their ceilings whenever they paint the walls. That’s usually every 5-6 years. If there are heavy smokers or a lot of cooking the ceilings need more frequent repaint. As always, we are always here to take care of your painting needs if ever you need us…but you’ve got this!