Here is the info on tap v's bottled water from the FAQ section
Tap water should be boiled for babies up to six months of age. After that it can be offered straight from the mains supply. If you wish to use a filter that is your personal choice, but do follow the filter manufacturer's instructions and keep filtered water in the fridge, as the filtering process removes some of the additives, such as chlorine, used to keep tap water fresh.
If you are travelling overseas, bottled water is the better option, as a different tap water could cause a tummy upset and diarrhoea, however safe it is in terms of cleanliness. Avoid those with a high mineral content and opt for still low sodium varieties, often labelled "suitable for infant feeding", such as Evian or Volvic. These should also be boiled when used for young babies, as they are not sterile.
It is worth mentioning that those few people with their own wells in the garden would be advised to get their water supply checked before their baby arrives. Certain private water supplies are high in nitrate levels and not recommended for babies' use. In this situation natural bottled mineral water would be the safer option, boiled and cooled first in babies below six months of age.
If you use water from a well instead of a community water supply, have it tested to make sure it is safe before using it for your baby. Boiling well water does not assure safety. The well could contain a high nitrate level which could harm your baby and boiling would concentrate that level. Call your local health department or Cooperative Extension office. They may test it or tell you how to find a company that will do it for you. Use distilled water especially when traveling and you do not know the safety of the water supply.
Reviewed March 2006
The information above is designed for educational purposes only. It is not intended to be a substitute for informed medical advice or care. You should not use this information to diagnose or treat any health problems or illnesses without consulting your pediatrician or family doctor. Please consult a doctor with any questions or concerns you might have regarding your or your child's condition.