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We’ve all heard the admonition, “Drink eight 8-ounce glasses of water each day for optimal health,” with a further warning that it must be water — not coffee, carbonated beverages, or other fluid sources. That amount equals two quarts or half a gallon of water daily. It’s hard to trace the source of the advice, or to find credible scientific evidence to support it. How are we even to know to whom this caveat applies — sedentary older folks or normally active people working in offices and exercising several hours each week? Young or old? People living in temperate or hot climates? Healthy or sick individuals? Athletes or couch potatoes? Nevertheless, it is common to see people in every category lugging around bottles of water, sipping and slurping throughout the day as they engage in their normal activities.
That’s a lot of liquid. For what reason? Because our bodies are about 60% water, supporters claim a wide range of health benefits from drinking such large quantities of water: reductions in cancer, heart disease, constipation, fatigue, arthritis, angina, migraine, hypertension, asthma, dry cough, dry skin, acne, nosebleed, and depression; improved mental alertness and weight loss. But solid proof is lacking for most of these.
Can there be harm from drinking so much water? Probably not, except for infrequent cases of causing a low sodium concentration in the blood, ingesting pollutants in the water, or maybe a guilty conscience for non-achievers.
So, how much water is enough? It depends…
Some situations require additional fluid intake:
- illnesses causing fever, vomiting or diarrhea
- living in a hot, dry environment
- high altitudes
- long plane flights
- kidney stones
- pregnancy or breast feeding
For the rest of us, if you rarely feel thirsty, and your urine color is normally pale yellow, you’re probably getting enough fluid. The fluid can come in any form: tap or bottled water, coffee, tea, soft drinks, milk, juices, beer (in moderation), and even in foods such as watermelon and spinach.
What advice is reasonable for healthy adults living in a temperate climate, performing mild exercise? Listen to your body! If you’re thirsty, drink. Advocates like to advance the dire threat that feeling thirsty means you’re already dehydrated. However, that alarm lacks credibility since feeling thirsty precedes actual dehydration, so there’s time to prevent it. If you’re not thirsty, there’s no need to drink, unless you fit one of the special categories mentioned above. We have enough worries in life without adding one more!