S.B.
My pediatrician recommended water when starting cup training, usually around 6 months. Baby will not get much to drink this way, but as cup training can be messy it is the best liquid to start with. Babies don't really need water until age 1 as long they get enough formula to drink, but if the weather is especially hot and baby has had enough formula we would give water from a cup (not from a bottle).
We held off on all food until 6 months, and then started with oatmeal instead of rice. Rice can be binding, causing baby to get constipated. Oatmeal doesn't have this effect, is very easy to digest, and is less likely than rice to cause an allergic reaction.
This worked well for my babies!