A method of making nonwoven fibrous materials suitable for use in a pollution control device or as a firestop, where the method comprises: providing a first slurry comprising water, first inorganic fibers, a first organic binder, and a first neutral pH flocculent; removing first waste water from the first slurry; optionally forming a first nonwoven fibrous material from the first slurry; providing a second slurry comprising a quantity of the first waste water, an optional quantity of relatively clean water, second inorganic fibers, a second organic binder, and a second flocculent that is the same and/or a different flocculent than that used in the first slurry; and forming a second nonwoven fibrous material from the second slurry. The addition of the first waste water in the second slurry does not adversely affect the flocculation of the second organic binder in the second slurry.