Giving too much water to babies under 6 months can be toxic? Doctor explains why you need to take precautions

Babies under 6 months have immature kidneys and cannot handle large amounts of plain water, so they should not drink additional water unless necessary.

Do you know you could harm your 6-month-old or younger baby if you give them more than a permissible amount of water? According to NHS surgeon and health content creator Dr Karan Rajan, who regularly shares educational videos on human bodies, various diseases and more, babies are not mature enough to adequately filter large volumes of plain water. Therefore, to keep them safe, we cannot give them a lot of water.

Dr Rajan’s video begins with a clip he stitched where a woman holding her baby in her arms asks, “Not to sound stupid, but can’t you just drink water to get hydrated?” Then, the text ‘No, I’ll die’ appears over the baby. Here's the science behind it:

‘Babies are not mature enough to filter large volumes of plain water’

“If you are in charge of a tiny human or you're about to be, this is one thing you absolutely need to know to keep your little biological Tamagotchis safe,” Dr Rajan says in the video. “As a general rule, exclusively breastfed babies under 6 months don't need any additional food or drink. Formula-fed babies under 6 months might need some additional sips of cooled, boiled water during hot weather, but not too much,” he explained.

As per the doctor, newborn babies have kidneys that are half the size or less of an adult, and they're ‘undergoing software updates’, so they're not mature enough to adequately filter large volumes of plain water.

‘Extra water can dilute the salt in the blood’

So, if babies can't drink too much water, how come breast milk has around 87% water and formula milk has around 85% water? “Crucially, both contain nutrients and electrolytes mixed in with carefully controlled amounts of water, which is safe for the baby. Giving too much additional water, either by over-diluting the formula or giving it separately, causes the extra water to dilute the salt in the blood,” Dr Rajan explained.

If the salt in the blood is diluted, it can lead to hyponatremia, a very low sodium level, which, in extreme cases, can result in brain swelling, seizures, and even death due to water intoxication. Moreover, adults can suffer from water intoxication, too, if they consume large volumes of fluid in a short space of time.

“However, for a baby, the margins are much smaller. Before the age of 6 months, this tiny human's stomach capacity is very small, and they have a slower gastric emptying rate than adults, meaning they get full very quickly. Giving lots of additional water means they may not have enough space for milk, which could lead to nutrient or energy deficiencies,” Dr Rajan said in the video.

Note to readers: This article is for informational purposes only and not a substitute for professional medical advice. Always seek the advice of your doctor with any questions about a medical condition.