Tap water through one of those pitcher filters is fine. It's super easy to spook new parents into buying stupid crap they don't need, out of fear.

So even if ten thousand of me said this a hundred thousand times, people would still buy the "special" bottled water with a picture of a baby on the label. You have to either just let them do it, or start bottling water and printing reassuring labels. They might wise up by the second or third kid.