Water spots are caused by leaks or prolonged condensation that collects between the floors of a building. The ceiling changes color as it soaks up the moisture. Over time, water damage can weaken a ceiling until it sags or even collapses, so it is important to detect and repair damage early. While there is no simple test to determine the age of a water spot, a few clues will help you develop a time frame.
Take into account the history of the building. A neglected building can harbor water spots for years. A well-kept home can receive extensive water damage following a sudden pipe burst or heavy rain, but unless you are out of town, you will notice the damage quickly. More often, water spots develop over a period of months due to insidious leaks from within the home.
Note the consistency of the spot. New water spots feel wet to the touch, but not soft. An older spot will feel mushy, as the drywall and ceiling have become saturated with water.
Note the color of the spot. One dark spot with no surrounding discoloration indicates a new leak. Rings of discoloration indicate that the area has been alternately soaked and then dried. As with trees, a greater number of rings indicates greater age.
Evaluate the size of the spot and the material the water traveled through. It takes time for a ceiling to absorb moisture and become discolored, so a large, multiple-ringed area will be much older than a single wet, clear spot. However, the composition of the ceiling and the amount of water trapped above the ceiling also affect the spot's size. For example, thick paint and tiles trap water, so even a small spot in a tiled ceiling indicates a longstanding buildup of water.
Look for mold. Moisture creates a hospitable atmosphere for bacteria, and materials such as drywall, carpeting and insulation are especially friendly to fungal growth. If bacteria has had time to set in, it means the water spot has been on the ceiling for at least two or three days. Warm temperatures and high humidity speed the growth rate of bacteria. A house in a humid, tropical area, for instance, will develop mold more readily than a house in an arid or freezing climate.
Check for rot. Decay doesn't generally set in after a first and singular instance of water damage, so any sign of rot means the structure has been exposed to either standing water or repeated flooding. The length of time it takes a building to rot will vary depending on the climate, temperature and humidity of your area.