For example, a basement that has flooded may appear to be dry after air-movers have been used, but unless the proper number of air-movers were used, along with the placement of them, AND use of properly-sized dehumidifiers, the moisture that was once present on the floor may remain behind the drywall and within other fibrous materials where it can remain hidden for days, weeks, or even months, until mold and/or mildew begins to form.