Hzatph wrote:

In my experience of water ingress, redecorating can be a pain - emulsion
paint does not cover the marks on the ceiling. You may be adviosed to use
primer or an oil based paint to sel it (when it it dry obviously) and then
you can use emulsion over the top.

....or seal with diluted PVA first. This will stop the water stain
coming through the new paint.

Andrew