I just googled this question and was horrified at the results. Most people, even "experts," seemed content instructing people to make their baby's formula with tap water. Some replies did suggest boiling it until the baby is at least six months old. (Which really only leads to feeding your baby possible dead organisms). Some suggested bottled water, but most people don't realize that bottled water is even less regulated than tap water. The more conscientious replies suggested using some sort of filtering method, but not one (that I could find) suggested the best possible source of healthy water for making baby formula: home distilled.
Essentially, the process of distilling water entails boiling water, collecting the steam (and filtering the steam to avoid any carry-over VOCs), and cooling. This might sound complicated, but luckily, there is a home distiller that works as easily as a coffee maker, and looks as stylish, too.
But why should you go to the "trouble" of distilling your water? It really isn't any trouble, but why bother?
Most people assume that if something doesn't kill you on the spot, it must be okay. Most people also assume that our water is regulated and that the government would NEVER allow unsafe water to flow through our taps. Both are wrong.
A short list of water contaminants which should concern you include heavy metals, pharmaceutical wastes, living pathogens, toxic industrial wastes, and even the chlorine added by municipalities. MOST of these things are not even regulated, so they don't even test for them. And then there are the things that they do test for and allow a certain amount before they are concerned. How much toxin should be allowed in YOUR baby's formula water?
Your baby is going to come in contact with toxins as it is; don't you want to remove the toxins that you can?
A home water distiller can be purchased for the entire family's use, and can be used as the baby grows into a child. You don't have to lug home water bottles, and you will actually SAVE MONEY in the long run. You simply use the "practically free" water from the tap and purify THAT. Easy peasy.
If you have any questions, please ask! I've been drinking home distilled water for a decade and love to convert other health seekers who want what's best for their babies!