Your baby will get all of his nutrition from breast milk or an iron fortified infant formula until he is four to six months old. There is no need to supplement with water, juice or cereal at this time. He will probably be eating every two to six hours and if feeding on-demand and following your baby's cues remember that not all cries are ‘hunger-cries' and you may have to set some limits (for example, not allowing to feed every hour).
Most breast feeding babies will eat for 10-15 minutes on each breast every 1 1/2 to 3 hours and formula feeding babies will take 2-3 ounces every 2-4 hours. By 4-8 weeks your baby should be on a more predictable schedule.
Feeding practices to avoid are giving a breastfed baby a bottle before he is 4-6 weeks old, putting the bottle in bed or propping the bottle while feeding, putting cereal in the bottle, feeding honey, introducing solids before 4-6 months, heating bottles in the microwave, or feeding goats milk.
Also, avoid the use of low iron formulas, which are nutritionally inadequate to meet the needs of a growing infant.
These types of infant formula do not contain enough iron and will put your child at risk for developing iron deficiency anemia (which has been strongly associated with poor growth and development and with learning disabilities). Iron fortified formulas do not cause colic, constipation or reflux and you should not switch to a low iron formula if your baby has one of these problems.