How do I get a water stain off a painted wall?

I've got this white stain on my wall. It was coming through the wallpaper, so I removed the wallpaper and painted over it. Now it's coming through the paint. It's a white stain higher up, and seems to have just darkened the paint farther down. I thought...

I sprayed some lysol on my painted wall and now theirs a big mark where the spray hit the wall. how do you get rid of it. it basically just looks 2 shades darker than the rest of the wall. thanks

My girlfriend has accidentally spayed perfume on our freshly painted bedroom wall,i have tried a damp sponge and water but its still there. Any suggestions??

The people who rented my apartment before me spilled all types of food on the walls and my landlord just painted over it! Is there a way I can get the stain off even though it's been painted over? Thanks!

Iv had pictures on a painted wall and when I took them off it left a small stain where the bluetack had been, How do you get rid of that? thanks