How do I remove a water stain on the ceiling of my living room?

first you need to find out where these stains are coming from. if this is a roof leak, PLEASE take care of quickly. if these are reoccurring, then no matter how much paint you throw at it this WILL come back! Next, if this is a 1 time event, then you can paint this ceiling with a nice latex paint and cover the FULL ceiling for an even color.

Check for leaks and get roof or pipes fixed. Put some Kilz over the area, let dry, smooth out any rough areas with sandpaper OR steel wool, clean off any dust, paint.

Indeed, find the source of the leak and get that fixed asap. I've found a mix 20/80 mix of bleach to water dabbed lightly with a paint brush clears up the stain. You can then prime and paint over the area.

You will have to find the source of the leak and repair it or the stain will reappear.

Once fixed, you can bleach out the stain with a combo of 1 part bleach and 4 parts water, dab with a paint brush that will fit the size of the task. Dab with plain water when the stain is gone and let dry. The prime with Kilz or Zinsser let dry and then paint.

Use a good primer, you'll probably need two coats and then paint. We recently found one from Benjamin Moore with low VOCs and it was waterbase, so it didn't smell and it worked great to cover our stain.