Forget the “eight glasses a day” rule. The amount of water your body actually needs depends on several factors, including your weight, activity level and the weather. Here’s how to estimate your daily intake and recognise when your body needs more.
The body weight formula
If you’ve ever wondered exactly how much water you should drink, a good place to start is your body weight. Many dietitians recommend aiming for 30ml to 35ml of water per kilogram of body weight each day.
That means someone weighing 60kg would need roughly 1.8 to 2.1 litres of water daily, while a person weighing 70kg would need about 2.1 to 2.45 litres. It isn’t a strict rule, but it offers a more personalised guide than the blanket advice to drink eight glasses of water a day.
According to Dr Melissa Prest, a registered dietitian nutritionist and spokesperson for the Academy of Nutrition and Dietetics, hydration needs vary from person to person because factors such as body size, physical activity, climate and overall health all influence how much fluid the body loses each day.
Why body weight matters
Water keeps the body functioning properly. It helps regulate body temperature, lubricate joints, transport nutrients, support digestion, remove waste through the kidneys and maintain healthy blood circulation.
Because larger bodies generally contain more water and have more tissue to support, they often require more fluids than smaller bodies. Body composition also matters.
Muscle contains more water than body fat, so someone with more muscle mass may need more fluids than someone of the same weight with less muscle.
Pregnant women, breastfeeding mothers, and people recovering from illness also have increased hydration needs that go beyond the standard formula.
When you need even more water
The body weight calculation is only a starting point. Several everyday factors increase the amount of water you need.
Living in a hot and humid climate like Lagos means you naturally lose more water through sweat, even without exercising.
If you’re physically active, experts generally recommend drinking an additional 350ml to 700ml of water for every hour of moderate exercise, depending on how much you sweat.
Illnesses that cause fever, vomiting or diarrhoea can also lead to rapid fluid loss. In those situations, oral rehydration solutions may be more appropriate than plain water because they replace lost electrolytes as well as fluids.
While coffee and tea contribute to your daily fluid intake, consuming large amounts of caffeine or alcohol may increase fluid loss for some people, making it important to stay adequately hydrated throughout the day.
Listen to your body
Numbers provide a helpful guide, but your body often tells you when it is getting enough water. One of the easiest indicators is the colour of your urine.
Pale yellow usually suggests you are well hydrated, while dark yellow or amber urine often means it is time to drink more fluids.
Contrary to popular belief, feeling thirsty does not necessarily mean you are already severely dehydrated. For most healthy adults, thirst remains a reliable signal that the body needs more fluids.
Other signs of mild dehydration include headaches, fatigue, dry lips, dizziness and difficulty concentrating. These symptoms are often blamed on stress or lack of sleep when dehydration may be contributing.
Making hydration easier
You do not have to measure every glass to stay hydrated. Instead, build drinking water into your daily routine. Have a glass when you wake up, keep a reusable bottle nearby throughout the day and drink a glass with each meal. If plain water feels unappealing, adding slices of lemon, cucumber or mint can make it more enjoyable without adding significant calories.
Hydration is not one-size-fits-all, and no formula can account for every person’s lifestyle. However, knowing your approximate daily water requirement gives you a practical starting point, making it easier to drink enough for your body’s needs rather than relying on guesswork.
