There are a lot of hydration myths out there – from the wild (drinking gallons of plain water daily) to the mundane (the classic “8 glasses a day” for all patients). But how much water do you really need in a day?
In general, most people need around 2-3 L of water per day (outside of the water content of our food intake) or about 9-12 eight-ounce cups of water daily, or about 4.5 to 6 of the standard plastic disposable water bottles daily. Men need a bit more than women, and children’s needs vary by age/body size.
A LOT of other factors play into your daily needs: your consumed fluids (liquids and foods), the temperature outside, your level of activity and how much is lost to sweat, your age and body size, medications that can cause you to lose more fluids (like diuretics) or that can lead to less of a drive to take in fluids (like GLPs), and more.
Thirst is a generally useful, though imperfect, hydration signal. For generally healthy adults, “drinking to thirst” – not necessarily drinking so much you’re constantly trying to prevent thirst, or drinking fluids on a rigid schedule – is a reasonable strategy, and leads to adequate hydration in most situations.
However, older adults often don’t experience thirst perception as well as younger adults and are at greater risk of dehydration relying on thirst alone. Children may not recognize or communicate thirst reliably, and they may require more prompting to maintain hydration, as well. Scheduled drinking is also preferred over drinking to thirst during intense or prolonged exercise.
Understanding Summer Hydration
Around 20% of daily water intake typically comes from food — meaning your diet is a legitimate and meaningful hydration strategy outside of plain water intake.
Electrolytes — particularly sodium, potassium and magnesium — are required for your body to retain and use fluid at the cellular level; water alone isn't always enough.
Hydrating Foods to Add to Meals
Consider adding these high water content foods to meals: Watermelon, strawberries, cantaloupe, lettuce, celery, spinach, cucumber, cabbage, squash (cooked), pickles, oranges, grapes, bell peppers, apples, pears, pineapple, carrots, broccoli (cooked), fruit juice, fat-free milk, yogurt, bananas, avocados, cottage cheese and corn (cooked).
Best Beverages
Water is still the best — add citrus slices or cucumber for palatability without added sugar. However, avoid excessive plain water during prolonged exertion. Drinking only plain water over extended exercise or heat exposure can dilute sodium levels and, in extreme cases, can cause hyponatremia; add electrolytes if you're sweating heavily for more than an hour.
Sports drinks are for sweating. Water is the main rehydration beverage of choice for most activities lasting <1 hour. For exercise over an hour or for heavy sweating, a sports drink with electrolytes and some carbohydrate (look for 6–8% carbohydrate and at least 100 mg sodium per 8 oz) helps replace what sweat takes away and keeps fluid in the body longer than water alone. These are designed for active hydration. There are many, many brands out there that vary in their composition. In my review, “Gatorade Thirst Quencher” meets these requirements.
Oral rehydration solutions (ORS) are indicated for significant dehydration. ORS remains the most evidence-based choice for significant dehydration from illness, heat exhaustion or significant fluid loss. The World Health Organization-formulated ratio of sodium and glucose is specifically designed for efficient fluid absorption.
WHO-recommended homemade ORS recipe is: ½ teaspoon of salt (3.5 g) and 8 teaspoons of sugar (40 g) dissolved in 1 L (about 1 quart) of clean water.
Pedialyte and comparable generics are great for children and adults.
What to Limit
Alcohol is a diuretic and accelerates fluid loss, particularly in heat. Skip it, and consider a hydrating mocktail instead.
Sugary sodas mainly contribute to excess calories. Water-rich foods and plain beverages are better choices.
Energy drinks are also not a good source of hydration, and excessive caffeine accelerates dehydration.
Practical Tips
Build hydrating foods into every summer meal to boost water intake, rather than relying solely on beverages.
In high heat or heavy activity, proactively add electrolytes.
Use urine color as a quick daily check: pale yellow indicates good hydration, while dark yellow or amber is a signal to drink more.
All this typing has really made me thirsty. Time to hydrate!
About Marielle Williamson-Rea, DO: Dr. Marielle Williamson-Rea(opens in a new tab) is a board-certified physician specializing in Family Medicine and Lifestyle Medicine, bringing a personalized, whole-person approach to primary care. She offers flexible office hours at her practice in Wexford, Pennsylvania, and direct support by phone, texting and email access.
