That should work. (Obviously don't mix up the water and bleach bottles! LOL!) I'd replace the bleach or top it off when it got down to about half so it doesn't lose it's dilution to the air in the bottle, but that should work well. Great idea. I may do the same thing. Thanks.
As long as you are "close enough" to the formula for the dilution you'll be OK. After all how close is measuring by "cap fulls"? No where near accurate as your measuring by calibrated "squirts" which have a fixed capacity.
Swordmaker,
Is it necessary to use other mouth rinse (for example Listerine) once you are on a regimen with the bleach/water blend? I imagine the bleach blend kills everything Listerine would? Or would you still recommend using a mouthwash and what brand and type? (Some use alcohol, some alcohol free, some use artificial sweeteners, others not).