Firstly, ensure that any possible cause of a leak has been found and fixed. For water-stains we recommend the use of Zinsser Cover Stain or Fleetwood Bloxx-It primer sealers. Apply two coats according to instructions. This will prevent the stain “bleeding” into your topcoat. Topcoat with any interior wall or ceiling paint.
For damp stains apply a breathable primer such as Ronseal Damp Seal or Toupret Humistop and topcoat appropriately.