In the summer, we all become a little more concerned with how much water we drink. Rather than forcing yourself to get through a bottle over the working day, you might find that you’re having to reach for a refill by 11am because you’re parched. But staying hydrated goes well beyond avoiding thirst. In fact, mounting evidence suggests that water is one of the fundamental nutrients required for good gut health.

A 2022 study, published in The Journal Of Nutrition, examined the link between hydration and gut health in over 3,000 people from the UK and US. It found that the gut microbiomes of people who drink a lot versus those who drink barely anything are different, with high-volume water drinkers having a lower abundance of campylobacter bacteria, which has been linked with gastrointestinal infection. 

This is the first time experts have examined the link between water and changes in gut composition. While more research is needed on the topic, it’s clear that water intake plays a key role in the make-up of our gut microbiome.

What we do clearly know is that dehydration can impact gut health. When we don’t drink enough fluids, we’re more at risk of constipation, says Sophie Medlin, leading dietitian and founder of CityDietitans. That’s because “the water in the body gets diverted out of the bowel for other essential functions, leaving the stool dry, hard and difficult to pass.

“Over the longer term, this can lead to disruption of the microbiome and even contribute to some medical problems, such as diverticular disease,” she warns. That’s a disease characterised by small lumps forming in the lining of the intestine which can lead to stomach pain (usually on the lower left side), constipation or diarrhoea, and occasionally blood in your poo. Those lumps can also become inflamed or infected. 

So, it’s really important that we drink enough. This isn’t about constipation in and of itself; chronic constipation can lead to more severe issues. As such, we shouldn’t ignore symptoms like pooing less frequently in the summer months or noticing that our stool is harder. When you do, Medlin says, it’s time to up the water intake.

“You are likely to feel more bloated and perhaps more gassy if you’re getting constipated, so look out for those signs, too.”

But what if you’re already aware of your gut health and, as such, are busy taking probiotics and fibre supplements to keep your microbiome happy? Anyone who’s had a slice of dense seeded bread or tried a teaspoon of psyllium husk will know only too well how moisture-sapping high-fibre foods can be. Can fibre actually make us more dehydrated and therefore (ironically) more at risk of constipation and poor gut health? 

“When we add fibre, particularly fibre supplements or things like chia seeds, without drinking enough water, it can lead to a drier, more bulky stool that causes even more trouble,” Medlin admits. “This is because fibre typically draws water to the bowel, making the stool softer and easier to pass, but when there isn’t enough water, it becomes a sticky mass that can slow things down even more in the bowel.”

In other words, if you’re upping the fibre, you’ve got to increase the water consumption. And that’s especially important during the summer. “Some people may well notice that they’re more bloated and constipated in summer months or when they’re on holiday in the sunshine. It’s important to remember that when you’re sweating or the temperature is higher, you need to increase your fluid intake,” Medlin explains. 

She says that an extra 500ml (or a pint) of water tends to be all we need to stay regular in the heat, but if sunny days tend to end in a beer garden, you’ll need to take extra precautions. “We have a tendency to enjoy a beer or a rosé in the sun, so make sure to match your alcoholic and caffeinated drinks with a glass of water to prevent excessive dehydration.”

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