If you see any of the following signs, you may have ceiling water damage:
1. Look for signs of water damage on the surface of the drywall, such as water stains, bubbling, or peeling paint.
2. Tap on the drywall. If it sounds hollow or makes a thudding noise, it could be a sign of water damage behind the drywall.
3. Use a moisture meter to check the moisture content of the drywall. If the moisture content is high, it could be a sign of water damage.
If you find any evidence of water damage behind drywall, it's important to have it repaired as soon as possible to prevent further damage to your home or building.