Hi Wayne
Purification of water is only necessary if your water source (ie well point) have impurities in it like iron, sulfur, too much magnesium or chloramines(tap water).
Babies are more susceptible to these impurities, and if they are present, the water should first go threw a filter designed for the specific impurities in that water source(ie an iron filter)
It is more applicable to other countries where the underground water is often not as good as ours.