When Can Babies Have Water? Safe Ages, Month by Month

No Water Before 6 Months — and Here's Why

For babies under 6 months, breast milk or formula provides all the fluid they need — even in hot weather. Giving extra water is not just unnecessary; it's dangerous. Infant kidneys are immature and cannot process large amounts of free water. This can dilute blood sodium levels, causing a potentially life-threatening condition called hyponatremia (water intoxication) (AAP, 2023).

If your baby seems hot or fussy in warm weather, the answer is more nursing — not water. The composition of breast milk shifts to meet hydration needs.

After 6 Months: Small Amounts Are Fine

Once solid foods are introduced, small amounts of water can be offered — primarily to introduce cup drinking rather than as a significant hydration source.

• 6–12 months: Up to 4–8 oz (120–240 ml) per day, offered in a small open cup or sippy cup at mealtimes.
• 1–3 years: 1–4 cups per day depending on activity and diet.
• Avoid juice: The AAP recommends no juice before 12 months — the sugar content offers no nutritional advantage over whole fruit.

Signs of Dehydration

Signs your baby is well hydrated: regular wet nappies (the NHS looks for around 6 a day in a formula-fed baby and at least 6 heavy, wet nappies a day from day 5 in a breastfed baby), tears when crying, moist mouth and lips. The NHS lists warning signs of dehydration as a sunken soft spot (fontanelle), sunken eyes, few or no tears, fewer wet nappies than usual, and being drowsy or irritable, and says to ask for an urgent GP appointment or call NHS 111.