Accidental humidity usually manifests itself for unforeseen or unpredictable causes, through a more or less accentuated isolated and circumscribed patch of humidity, accompanied by a halo.
If the stain concerns the masonry we will probably notice a swelling and a possible detachment of the plaster. The same can happen with wooden floors.
The planks will be curved and detached from the support due to involuntary contact with a quantity of water poured onto the floor in an unwanted or unexpected way over time.
It can generally come from: leaks from plumbing and water pipes, damage to downpipes, breakage of pipes and sewers of sanitary and sewage systems, leaks from the roof, cracking of sheaths, broken tiles due to the involuntary passage of some operator or because of strong hailstorms, broken water tanks and the heating system, forgetfulness and human errors, etc …
Accidental humidity can also be caused by breakage or malfunction of appliances that use water, such as washing machines and dishwashers.
The only effective solution in case of accidental humidity is the repair of the fault that is at the origin of the leak.
Often, however, action is taken by treating only the surfaces (for example by restoring the plaster and repainting) to hide the damage, but it is an unnecessary and often counterproductive operation for identifying the real problem, which punctually reappears.
Most of the time visual control and common sense are sufficient to recognize problems related to accidental humidity.
In cases where visual inspection leads to dubious results, some advanced diagnostic tools, such as infrared thermography, can be used. A broken water pipe can be easily identified by an infrared camera by taking advantage of the temperature difference between the cold floor and the spraying of hot water from the broken pipe.
The most appropriate procedure to solve the problems caused by accidental humidity is to first recognize the cause (with visual or instrumental investigation) and act directly on that, and then subsequently also restore the damaged finishes (which are a symptom, not the real problem).