- it is easy to use way too much bleach, wasting money, causing skin/eye/nose irritation, putting more chlorine in wastewater; and,
- the pH of bleach in water is too high to disinfect to its full potential. In other words, disinfecting with plain bleach is leaving money on the table. When the pH is not adjusted there is more bleaching going on than sanitizing. Think about that next time you use bleachwater on that grout or the board where you cut that chicken up.
Here's the 2nd trick, dropping the pH of the solution down from 8+ where it is now down into the 6.5-7.5 range where it works as a viciously-effective sanitizer but does not generate chlorine gas. The way to to this is to add 1 fluid oz of normal white vinegar to your mixed bleachwater. Of course you know not to mix those undiluted chemicals, right?
That's why it's called 1ozBWV; the amounts are in the name (1oz) and the order of addition is specified: Bleach first, then water, then vinegar.
This method was most famously described by Charlie Talley, a chemical engineer formerly responsible for production of Clorox bleach. He currently produces a nonbleach sanitizer for the homebrewing market. For more information, listen here.