Water and the Conservation of Mass
Sorry if this is a recurring nightmare of yours, but we'd like to take you back to middle school science class for a second.
Specifically, we want you to think back to the day that you learned the "law of conservation of mass."
Don't remember it? Here's the Cliffsnotes: matter cannot be created nor destroyed. Mass is always conserved in any closed system.
Why are we bringing this up in the context of water damage? Because it can be a difficult thing to remember when your house floods.
Consider this example: John has a pipe burst and his kitchen floods with 50 gallons of water. John calls SERVPRO, who comes out the extract the standing water, which totals 30 gallons.
John doesn't see any remaining water, so he assumes that he's all set.
But that remaining 20 gallons of water cannot simply disappear. It had to go somewhere. And barring some kind of magic, it's safe to assume that it's still in John's house somewhere.
Most likely, that water has migrated into structural materials, like under the floor and into the walls. Some may also have evaporated into the air, causing humidity levels to rise.
Finding the hidden water and dealing with it is where the real work of water damage restoration begins. Just because you can't see it doesn't mean it isn't there - that's what the law of the conservation of mass teaches us.