I always assumed it was in our tap water though lol.
Fluoride is good for your teeth when it's in your both. If you're just drinking it, then it can pose other health risks to your body. At low levels that's not a problem, but some research suggests that there's likely too much fluoride in some drinking water systems and it's doing more harm than good.
I'd recommend brushing your teeth with a fluoride toothpaste, but I personally would prefer not to drink fluorinated water and I wouldn't swallow my toothpaste. And the "don't rinse" shyt sounds suspicious - besides causing you to swallow more fluoride, it also seems like it would clear less of the bacteria from your teeth.
Maybe this guy knows what he's talking about, but I'd like to see receipts. Just because he's a dentist doesn't mean he reads the studies, and the day-to-day work of being a dentist wouldn't be able to show him whether rinsing or non-rinsing is better. He could still just be going off of assumptions rather than research.
I tend to be suspicious of specialists when the main drawbacks to what they are advocating are outside of their area of specialty.