Stains on your ceiling is a sign of water leaking above it. This water can come from a few locations but is most commonly from your plumbing or a leak in your roof. Water can cause many issues and should not be neglected, even it's a small stain. The stain is just the tip of the issue as you may have had a leak for a while and the water is just now getting to the ceiling and may have already caused water damage or mold growth.
Don't Cover it up Without Repairing the Cause
Typically unknowing homeowners will see an ugly stain on their ceiling and just use paint to cover it up and it would be a big mistake. There are a few reasons to address the cause first before covering the stain. The first would be that the stain is a sign of a leak and a water leak should be repaired as soon as possible. This article has already mentioned that the water leak may have traveled from the source of the leak to the stain and already caused water damage and/or mold growth and I mention it again here to stress the importance of repairing the damage and removing mold. Mold is a fungus that absorbs organic material as it's nutrient source, which the organic material in this scenario being wood means the wood is getting broken down and the structure of your home is being compromised. Similarly the water damage in this case would be warping, cracking, or rot from mold breaking it down and the water damage could also cause structural damage.
Common Causes of Water Stains
There a few common causes of water stains that you should check out to find the source of the water. Check these causes first before you waste time, resources, and money looking elsewhere, however you should be aware, that just because you found a leak or what you suspect is the cause of the water stain, doesn't mean there isn't another cause or an area that may be a problem soon. Use this opportunity to check on the health of your house while you already have the area open.
Leaks
Leaks can come from a few different sources. Leaks won't be easy to find as simply finding water. The water from leaks can be absorbed into the wood or surrounding material. There are some tools that can help identify leaks such as a moisture meter, but if you don't have access to such a device you can look for signs such as smells, discoloration, warping, cracking, or soft wood. Below are areas to look for leaks:
Bad Seals
Toilets, pipes, and appliances have connections where a bad seal can result in a leak. Toilets have the seal between the toilet and the drain pipe and also a water line connection. Pipe connections should be checked for loose seals, and you should check the water turn off valves. Appliances should be checked where the water line is connected to the appliance. Don't forget to check under the sink and cabinets for leaks
Pipes
Besides a failing joint or connection, a pipe may have a small tear causing small amounts of water to leak out and travel along the pipes or wiring.
Roofing
Roofing is exposed to rain and snow and if there is a small opening or tear, water can get inside and may pool where the opening is, or it may travel along pipes, wiring, or any other surface that doesn't absorb water. Just because there is a stain on the first floor, doesn't mean the stain couldn't be caused by a roofing leak.
Ventilation
You may not have obvious ventilation and the hidden ventilation may not be fully sealed tight and is allowing water into the home. Improperly installed ventilation may also cause some condensation to accumulate and fall back inside your home.
Condensation
If your home is not properly insulated and has poor air circulation, you may have condensation build up on the coldest area in your home. The condensation can accumulate and fall down onto the ceiling causing a water stain.
Humidity
High levels of humidity can be a cause for water stains on your ceiling. This could be caused by poor ventilation, as mentioned above, or from too much moisture in the air such as from cooking, showering, and laundering clothes. Humidifiers can help reduce the level of humidity in your home.
Ice Dam Leakage
An ice dam is a ridge of ice that forms at the edge of a roof and prevents melting snow from draining off the roof. The water that backs up behind the dam can leak into a home and cause damage to walls, ceilings, insulation and other areas. The water from the leak may travel along the insulation then run down and onto the ceiling causing a stain. To prevent ice dams, check if there is an area of your roof where snow doesn't melt as fast and if there is, proper insulation should be used and be sure not to block ventilation areas.
Malfunctioning Appliances
Some appliances can cause leaks and should be checked on during your home maintenance checks. This could be air conditioning units, hvac systems and ventilation, dishwasher, refrigerators, washers, and any other appliance with a water line hookup.
Water Stain Cleanup
Water Stain Cleanup: If you have found the source of the water stain and fixed it, then you can begin to clean up the water stain. Water stains can be cleaned up with everyday household items and chemicals. To start, use a damp cloth to remove any excess moisture from the area and then let the area dry completely before continuing.
Once the area is dry, use a sponge to apply a cleaning solution of equal parts white vinegar and water. The acidity in the vinegar will help break down the stain. Let it sit for 5 minutes before wiping it away with a damp cloth. If you still see any discoloration, you can try using baking soda on the stain (mixed with water to form a paste).
Please note to check your solution on an inconspicuous area first to check if the solution of chemicals and water will affect the coloring of the ceiling's paint.