On a hot day, most people wait for one signal before reaching for water, or thirst. It feels intuitive. After all, your body should tell you when it needs something, right? Not quite. Doctors say thirst is not always the reliable indicator we assume it to be, especially in summer when fluid loss is higher and faster.
According to Dr Pooja Pillai, Consultant in Internal Medicine at Aster CMI Hospital, Bengaluru, “Thirst is often a late signal. By the time you feel thirsty, your body may already be mildly dehydrated.”
Why thirst alone isn’t enough
The body loses water constantly, through sweat, breathing, and even digestion. In cooler weather, this process is gradual. But in heat, it speeds up significantly. The problem is that your brain doesn’t always keep up. “Thirst signals tend to lag behind actual fluid loss, especially during hot weather or physical activity,” Dr Pillai explains.
So while you may feel fine, your body could already be running low on fluids.
When drinking “on demand” still leads to dehydration
It sounds logical: drink when thirsty, stop when you’re not. But that approach can quietly fall short. In high temperatures or humid conditions, the body loses more water than it signals for. Add to that factors like caffeine intake, illness, or even age, and the gap widens further.
“Some individuals may still remain mildly dehydrated even if they respond to thirst, because the body has already lost fluids before the signal appears,” says Dr Pillai. This is why hydration needs to be a little more intentional, especially in summer.
Who needs to be extra careful
Not everyone experiences thirst the same way. Older adults, for instance, tend to have a weaker thirst response. Children may not recognise or communicate it clearly. And certain medical conditions, like diabetes or kidney issues, can affect how the body manages fluids.
“People in these groups are more likely to become dehydrated without noticing it,” Dr Pillai notes, adding that regular fluid intake is essential for them, regardless of thirst.
What proper hydration actually looks like
So if thirst isn’t enough, what should you rely on? Experts suggest building small, consistent habits instead of waiting for a signal. Drink water at regular intervals. Keep an eye on urine colour; pale yellow usually indicates good hydration. Increase intake when you’re outdoors, exercising, or exposed to heat for long periods.
“Hydration should be proactive, not reactive,” says Dr Pillai. Including natural fluids like coconut water or buttermilk can also help, along with water-rich foods such as cucumber and watermelon.
Thirst might be your body’s way of asking for water, but it’s not always timely. In summer, especially, waiting for that signal can mean you’re already playing catch-up.
