argh, not this!
Right, misconception clear-up time.

Bottled water in many cases is just bottled tap water. Nestle's brand over here, and 'oasis' from dubai, is just bottled tapwater, nothing else.

Tap water contains chemicals.
Yes it does, thankfully, otherwise it wouldn't be water. It is made up of the elements hydrogen and oxygen, which are chemicals. It may also contain trace elements and a small abount of chlorine to prevent bacterial growth, boiling tap water will remove the chlorine.

Bottled water is safer.
Don't be too sure, Mineral water can only be classified as mineral water by the EU if it has had nothing added to it, that includes anything that will disinfect the water, which WILL contain a small bacterial culture.
Secondly, read this
http://www.rd.com/your-america-inspiring-people-and-stories/rethink-what...
It's a fairly good laymans summary of standards testing and safety of bottled water.

Either boil the tapwater or breast feed your child, I'm supprised you're not doing the latter since breast milk contains antibodies which will give your child limited protection against illness.
Your health adviser gave you qualified advice, try listening to her, the qualification means something.