What should you do to stay properly hydrated?
Drink when you are thirsty, have water with meals, monitor urine color (aim for pale yellow), and increase intake during exercise, hot weather, or illness. For most healthy adults, thirst is a reliable guide.
The simplest hydration strategy: keep a water bottle accessible throughout the day and drink when thirsty. Have a glass of water with each meal. If your urine is consistently pale yellow (like light lemonade), you are well-hydrated. Dark yellow or amber urine suggests you need more fluid.
Increase water intake during physical activity (an extra 500-1000ml per hour of moderate exercise), in hot or humid environments, at high altitude, when ill (fever, vomiting, diarrhea increase fluid losses), and during pregnancy or breastfeeding. The exact amount varies by individual — use thirst and urine color as your personalized guide rather than following a generic prescription.
How much water do you actually need per day?
The National Academies of Sciences recommends approximately 3.7 liters (125 oz) per day for men and 2.7 liters (91 oz) per day for women from all sources — including food and all beverages, not just plain water.
The popular '8 glasses (64 oz) a day' recommendation likely originated from a 1945 Food and Nutrition Board report that suggested approximately 2.5 liters of daily water intake — but also stated 'most of this quantity is contained in prepared foods.' The second half of this statement was lost over time, creating the myth that you need 8 separate glasses of pure water.
Approximately 20% of daily water intake comes from food. Water-rich foods include watermelon (92% water), cucumbers (95%), strawberries (91%), lettuce (96%), and soups. All beverages contribute to hydration, including coffee, tea, milk, and juice. The key is total fluid intake from all sources combined meeting your body's needs, which vary significantly based on body size, activity level, climate, and health status.
What happens when you are dehydrated?
Even mild dehydration (1-2% body weight loss) impairs cognitive function, mood, physical performance, and increases fatigue and headaches. Chronic mild dehydration may contribute to kidney stones, urinary tract infections, and constipation.
A 2012 study at the University of Connecticut found that mild dehydration (just 1.36% body weight loss in women) caused headaches, fatigue, difficulty concentrating, and worse mood — without subjects feeling particularly thirsty. In men, similar dehydration impaired working memory and increased anxiety. These effects occurred at hydration levels commonly experienced during daily life.
For physical performance, a 2% body weight loss from dehydration reduces endurance capacity by up to 25% and decreases strength and power output. In hot environments, dehydration impairs the body's ability to regulate temperature, increasing heat illness risk. Chronic mild dehydration is associated with increased kidney stone risk (the single most modifiable risk factor for kidney stones is fluid intake), higher UTI rates, and constipation.
Do certain beverages hydrate better than others?
A beverage hydration index study found that milk, oral rehydration solutions, and orange juice hydrate slightly better than plain water due to their electrolyte and calorie content. Coffee and tea hydrate nearly as well as water despite caffeine content.
A 2016 study in the American Journal of Clinical Nutrition introduced a 'beverage hydration index' comparing how long different drinks maintain hydration. Skim milk, full-fat milk, and oral rehydration solutions had the highest hydration index — their sodium, potassium, and calorie content slowed gastric emptying and improved fluid retention. Water, tea, and coffee were moderately hydrating. Beer and caffeine-containing beverages still produced net positive hydration.
The myth that caffeine causes dehydration is outdated. While caffeine has a mild diuretic effect, regular coffee/tea drinkers develop tolerance, and the fluid in these beverages more than compensates for any increased urination. A PLoS ONE study found that moderate coffee consumption (4 cups/day) produced equivalent hydration to the same volume of water in habitual coffee drinkers.
When do you need electrolytes in addition to water?
Electrolyte replacement is important during prolonged exercise (>60 minutes), heavy sweating, illness with vomiting or diarrhea, and in hot or humid climates. For normal daily activity, a balanced diet provides adequate electrolytes.
Sodium is the primary electrolyte lost in sweat, at an average rate of 900mg per liter. During prolonged exercise or heavy sweating, replacing only water without sodium can dilute blood sodium levels, potentially causing hyponatremia. Sports drinks, electrolyte tablets, or salted foods with water all effectively replace lost electrolytes.
For most daily activities, you don't need special electrolyte drinks — a normal diet provides more than enough sodium, potassium, and magnesium. Marketing has created unnecessary demand for electrolyte products during routine exercise. Reserve electrolyte supplementation for: exercise lasting more than 60-90 minutes, exercising in hot or humid conditions, heavy sweaters, and recovery from illness involving fluid loss.
