This will freak some people out here, but it's OK to chew gum, brush your teeth, or use mouthwash while water fasting. You don't want to be a giant douchebag while you are fasting. You are already going to get grief from coworkers and family and there is no reason to give fasting a bad name.
Don't chew gum with aspartame. There are brands with Zylitol that you can find at health stores. Spry is one brand.
Rinse your mouth out with water after brushing or using mouthwash so there are no residual chemicals to absorb.
An organic deodorant is also recommended. Tom's of Maine has some that you can get at Trader Joe's.
These things will not effect your fast in any significant way whatsoever. I have done many fasts both ways and the only difference is that with a piece of gum you'll keep your family and friends (and job in your case).. If you want a truly pure water fast, you should not be working. You should extract yourself from society and just lounge. In this case, it's OK to stink. But for those who wish to fast and still try to maintain their job, school, or whatever, don't be afraid to practice some hygiene.