Because so many people are drinking bottled water instead of tap water, studies are now showing that children are having more an more dental problems. Tap water is filtered, then fortified with certain minerals and chemicals aimed to improve our health, not hurt it, unlike spring water which has so many raw minerals, it can be harmful to the unborn child. Anyway, one of the chemicals added to tap water is fluoride. Studies have shown that children who were given tap water during pregnancy and after birth as well have much healthier teeth.
I am not saying that for this reason alone, all women should continue drinking tap water. But keep in mind not all the chemicals added to it are bad.