Fully breastfed babies don’t need any water until they’ve started eating solid foods.Once you have started weaning (4-6 months), due to this hot weather, do give some water after a solid meal, atleast 3 times a day. Milk is mostly water, so you don’t need water with it.
For babies under six months, use water from the mains tap in the kitchen. You will need to boil then cool the tap water as it’s not sterile straight from the tap. Water for babies over six months doesn’t need to be boiled.
Bottled water isn’t recommended for making up formula feeds as it may contain too much salt (sodium) or sulphate.