A leaky faucet does not meet the definition of a hidden defect as the buyer would not have backed out of the transaction had they been aware of the fact. This is not a major concern preventing the occupants from using the residence as they normally would.
By contrast, if there is—or has been—an undeclared water infiltration issue, it might constitute a hidden defect. Water can seep in from the roof, foundation, or a faulty drain. The consequences can be both disastrous and expensive. Moreover, if the foundation is affected below ground level, the issue is undetectable until it leads to very serious problems.
In any case, water infiltration can cause extensive damage and quite a few headaches!
The source of this issue is sometimes caused by an unresolved water infiltration problem. Uncontrolled indoor air humidity levels over a long period may likewise contribute to the spread of mould.
Dishonest real estate owners can use all kinds of tricks to conceal the presence of mould. For example, by applying thick layers of paint or by covering it with drywall, making it difficult to detect with the naked eye when viewing a property for sale.
Not to mention that mould can lead to serious health problems, usually affecting the respiratory system. These are often more severe in children, the elderly, and people who are already in poorer health.