The reason that you have stain on wall and ceiling is that the water left a iron residuw and when painted with water baced paint the stain reapears . If you put two coats of varnish over the stains leaving 24hrs betwean coats. Let it dry for 24hrs then repaint that should stop stain reapearing.
The most common cause is a water leak, especially in ceilings. A slow leak in your pipework, or a leaking radiator, could be feeding the stain and causing it to turn that horrible brown, typically caused by rust somewhere in your water system.