When can my 9month old stop drinking the purified water and start drinking faucet water?

Now: You can use municipal tap water for drinking water for babies as soon as they are old enough to drink water (around 6 months). If using water to mix formula, continue to follow the instructions on the package about water source and handling.

Tap water: There is no reason why you should not give your nine-month-old baby tap water to drink. Advice differs as to when it is safe to do this. Most sources do agree that it is necessary to sterilize babies' utensils and use cooled boiled water until a baby is over six months of age. Here is a link for you: http://www.babycentre.co.uk/x562089/when-can-i-stop-boiling-tap-water-for-my-baby

?water source?: If you live in a city with a monitored/superior water supply and have no concerns about tap water for you, there is never a need to use specialty water for infants. If you have a well, or concerns about the source or the plumbing I would avoid it at any age.