Your baby does not need water for the first 6 months of life as only breastfeeding or formula-feeding is enough. Milk contains enough water to quench their thirst.
Post 6 months, when you start feeding them solid foods, it’s okay to introduce water in small quantities. Try to give them water in a sippy cup, straw cup, or open cup from the beginning.
A few ml or oz of water during or after solid feeding is recommended and can be gradually increased to 1-2 small glasses of 250 ml water between 6-7 months. Water amounts may also vary if you live in extremely hot regions.