How much water do you really need?

It seems like every day, we hear that consuming eight glasses of water a day is best. But is that really the case? Not necessarily. In a recent study performed in Australia and published in the British Journal of Sports Medicine, dehydrated athletes who simply think they’re being rehydrated adequately perform no differently in physical trials than athletes who are actually re-gaining all the water they lost previously.

Worse, over-hydration can cause a phenomenon called hyponatraemia, or the dilution of necessary sodium in the blood. Without sodium, the cells in the body can’t communicate with each other effectively. Just like being low on electrolytes (of which the blood salt level is an important component) can cause cramps and muscle weakness, so can hyponatremia. Symptoms include fatigue and confusion, but that can lead into kidney failure, heart failure, or pneumonia.

So, how much water do you really need? Well, it depends on how much you work out, and what your lifestyle is like outside the gym. Exercising for an hour every day will cause you to sweat out as much as a pint of water, which can easily be replaced. It’s a good idea to keep water with you during your workout, so you can take occasional sips when you need it. And while you may carry that water in a bottle, the water itself need not be bottled. You can use your tap, provided the water in your area is safe. (Your teeth will thank you for that extra dose of fluoride.)

But if you consume foods with a large amount of water in them, that counts too. Foods like watermelon, cucumber, leafy greens, and celery have a large amount of water in them already. And coffee, tea, and other drinks also count toward your daily total water intake. This means that soups, smoothies, and juices can also effectively hydrate you.

On the other hand, foods prepared with a great deal of salt and sugar can dehydrate the body. Have you ever noticed that a cold glass of milk is exactly what a piece of chocolate cake needs? That’s because the sugar in the cake is parching your tongue. Or have you ever noticed that a big order of Chinese takeout means puffy skin the next day? That’s your body retaining water to deal with all the sodium it just took in. So: if you eat too much salt or sugar, your body may need more water, and it may retain that water a little longer than usual if the dehydration is persistent. And that can throw off your scale — water retention can drive up your weight measurement by a few pounds. So remember that the next time you eat foods high in salt or sugar, drink an extra glass or two of water to counteract the water retention, and help your body digest the food more effectively.

So, how much water should you drink? Drink the amount that quenches your thirst. When you’re thirsty, drink. If it seems like you’re thirsty all the time, consider how much sneaky sodium there might be in some of your food. And consider keeping a glass of water beside your bed to drink every morning when you wake up, to get your metabolism going first thing.