With this hot weather in Europe, it is the right time to discuss how much water a baby needs. Per kg of body weight the fluid requirements of a baby is much higher than and adult, but because of their smaller size they can dehydrate much faster than adults (not only with hot weather but also with diarrhoea and/or vomiting). So it is important to provide sufficient liquids.
As a rule of thumb during the first 6 months of life, breast milk or formula milk will not only provide all nutrients but all liquids. So the general advice is that the fluid up to 6 months of age, even in hot weather should ideally come from breast milk or formula milk. You may find that they want to breast feed more frequently and demand more formula feed, which is normal when it is so hot. Of course it is important to keep your baby cool and use current guidance on what to do when the weather is hot (including using sunscreen) with your baby.
For children > 6 months of age, breast milk/formula volume reduces as it is being displaced by solids (which is normal), so they will need additional fluid and the demand increases, the hotter the weather. The additional fluid should be in the form of cooled boiled water and fruit juices should be avoided. Of course the question is now to how much should a baby be given when it comes to water? Fluid requirement in theory is driven by the weight of the child; meaning you provide x amount of ml per kg of body weight (< 6 months around 120 ml/kg, > 6 months to 10 kg around 100 ml/kg). This is of course is easier said than done especially if a baby is breastfed, as you have no idea how much fluid your baby is drinking and although its easier to calculate that with bottle feeding, its difficult to establish how much fluid they get from food, as food (i,e, fruit, vegetables) also contain fluid.
So I suggest a pragmatic approach and recommend as a good starting point 20 ml after each meal (not before to avoid displacing food) and then to provide water during the day depending on the temperature (at the same low volumes). You may find your baby demanding more water and then it is fine to slowly increase the amounts. What I would certainly not recommend is big volumes like 100 ml given all at one go, which may displace breast milk or formula milk.
I also would recommend to give the water in a beaker that is free flow (either spout or open) so that your baby can manage to consume sufficient amounts. Check out for signs of dehydration which include:
- a sunken soft spot (fontanelle) on their head
- few or no tears when they cry
- fewer wet nappies (nappies will feel lighter)
- being drowsy
Finally, enjoy the summer, this is a wonderful time to enjoy lots of fresh fruits and vegetables.