As a professional cheesemaker, (yes, one of the blessed variety), the first question that comes to my mind is:
Why are these people throwing out their brine? This seems an unnecessarily costly exercise.
It is typical practice in many cheese factories (and all of those in which I've worked) to keep and re-use brine (sometimes for decades), with routine and simple maintenance such as topping up salt levels, adjustment of pH, filtration to remove solids and occasional pasteurisation if required.
A "raw" brine of just NaCl and water will, of course, do the job of salting your cheese, but most of the salt is left in solution at the end of the brining process (so it doesn't make sense to throw it away), and the pH will have a tendency to bounce around, adversely affecting the properties of your cheese. The various whey products in a re-used brine help to stabilise the pH, so one usually only needs to top up salt to replace that absorbed by the cheese.