At a population level, yes, toothpaste is enough. But you have to be diligent about brushing your teeth and going to the dentist. For those who don’t have access to neither, fluoride in the water was the best way to make sure they had consistent fluoride exposure. If you’re going to well water, would you have a way to test it for naturally occurring fluoride? It’s common in volcanically active places, like Central America. But your mileage may vary.