Well, when my son was 8 weeks old he was crying constantly and eating 6-8 ounces every two hours. So i started adding 1-2 tblspoons of baby rice cereal to his bottles a couple of times a day. I told my doctor at his 2 month appointment and he said that was absolutely fine and that a mom knows sometimes better what her baby's particular needs are. I introduced baby cereal on a spoon when he was 3 months and he did excellent with it, he then started baby food (stage one) at 3 1/2 months and is 6 months now and i started him on juice. my doctor approved all of this...you can easily try things out to find out how your baby handles different food types. I have given my son water from the start though he doesnt like it much.
all babies are ready at different times. my third and last is9 weeks old,and ive been giving her up to 8 ounces aday1/1 juice 1/2 water for about a week now! she's tolerating it great. i would start out a couple ounces at 1st and wait afew hrs. and see how she tolerates it. thats my advice. from, experienced mom.