WATER USED SIGNS ON THE CEILING
If you find signs of dried water on the ceiling of the house, this is a sign that there is water leakage seeping from the roof or tile, which is the outermost protection of a house. For that, there must be countermeasures taken. One of them is checking the roof or tile, to find out the origin of the water that causes the leak to seep into the ceiling.
A common cause of leaks is due to cracked or broken roof tiles. It could also be, a damaged gutter, or leaking seepage from an adjoining neighbor's house. If the source has been found, then repair it immediately by replacing the tile or lining the walls of the house and the area around the seepage area with a leak-proof coating.
If your ceiling is a product of cement board (fiber cement board) such as GRC board, then repair by sandpapering it until the watermark is gone. Then just paint it again to cover all the surfaces that have been sanded. For the record, the ceiling made of GRC cement board will remain strong and not rotten even though it is exposed to water seepage. Unlike other basic materials, the GRC cement board is high moisture resistant and anti-mildew which has the potential for the ceiling to become rotten.
Make sure, always use flagship products from the GRC board in your home building.